Article Original Article

Estimating Occult Timing of Surprise Gunshot Sounds in Silent Film via Observed Start of Human Voluntary Reactions of Concern Brian Roselle1 & Kenneth Scearce2 1Fairfield, OH, USA 2San Francisco, CA, USA

Abstract Article Information Voluntary human reactions, and associated perception times when reaction movements commence, are iden- Received: 2 March 2019 tified to estimate gunshot sound arrival time to subjects in a shooting scenario recorded on silent film. Com- Revised: 23 January 2020 mon involuntary reactions (startle) and voluntary reactions are reviewed to help identify proper reaction Accepted: 29 January 2020 types being observed and apply in back-calculating gunshot timing. With a focus on voluntary reactions, Published: 8 August 2020 values for perception time as a function of stimulus expectancy, specifically in the case of a surprise stimulus, Citation: Roselle B, Scearce K. Estimat- are determined by reapplication of brake perception-reaction time (brake PRT) modeling of extensive driver ing Occult Timing of Surprise Gunshot Sounds in Silent Film via Observed reaction time studies in traffic flow theory. Using a modified model in conjunction with sampling human Start of Human Voluntary Reactions reactions observed on film allows back-calculating surprise gunshot sound timing. To detail use of this of Concern. J Assoc Crime Scene approach, a well-known example of a silent film, the Abraham Zapruder film of the Kennedy shooting, is Reconstr. 2020;24:1-22. considered to help identify the first shot timing in that case.

Author contact: Keywords: chronology, gunshot timing, perception-reaction time, perception time, surprise voluntary [email protected] reaction, startle reaction, Zapruder film, shooting reconstruction, crime scene reconstruction, forensic science [email protected]

Introduction An integral part of overall crime scene throughout the scene and are often critical to reconstruction is determining the chronological the overall analysis”. timing of events. When investigating crime A parameter that can be useful in the timing scenes involving gunshots, understanding analysis of crimes, and a particular focus in this overall event timing is necessary and report, is that of human reaction time. “reconstruction is most effective when a Human reaction time studies which have comprehensive approach is taken including helped advance perspective on many timing consideration of events before, during, and related questions date back to the beginnings after the shooting incident” Chisum & Turvey of human study as a science. In 1862 the [1]. Further Gardner & Bevel [2] state that eminent Swiss scientist Adolph Hirsch used “to ignore aspects of chronology (timing and a chronoscope to show that human reaction sequencing aspects) in crime scene analysis is to times varied slightly between auditory, tactile, ignore what is often half of the data available to and visual stimulation as well as varying us. Timing and sequencing relationships exist between individuals. They were also dependent

J Assoc Crime Scene Reconstr. 2020:24 1 www.acsr.org on stimulus expectedness. Hirsch’s insights the impending stimulus, a particular challenge helped to explain and understand the variability in forensically evaluating reaction time to in, and between, astronomers’ reactions in loud stimuli like a gunshot on silent film is to measuring the exact transit time of stars viewed determine the subject’s level of expectedness to in telescopes [3]. Later F.C. Donders (1868) and it. Expectedness can range from very highly then Wilhelm Wundt (1879) further explored expected to totally unexpected (i.e., a complete measuring the time from an auditory stimulus surprise), and levels in between those extremes. to a voluntary reaction in response, in what was In many cases it is possible, from the context of called mental chronometry [4,5]. silent film, to be fairly confident that reactions The purpose of our report is to apply are surprise reactions, in that there is no the science related to human reaction time, anticipation or pre-knowledge of the stimulus, specifically based on brake perception- but in other situations stimuli may not be a reaction time (brake PRT), to crime scene surprise, making it difficult to estimate or assign reconstruction and forensic analysis. This a mid- or intermediate-level of expectedness or is achieved by applying a modification of a awareness to the ensuing stimulus. The approach modern brake perception-reaction time model described here is therefore limited to cases where (taken from automobile driver reaction time reactions observed can be readily classified as studies in traffic flow theory) to evaluations voluntary reactions to a surprise stimulus. As of silent film which include surprise voluntary surprise reactions can be involuntary startle reactions. The approach is developed as a way or voluntary in nature, distinctions between to improve estimates of stimulus (primarily these types of reactions are briefly reviewed as gunshot) arrival time to human subjects, from reference. film and video which lacks audio but displays In this report a subject’s stimulus arrival time individual reactions which can be classified will be a reference film frame number or film as surprise voluntary reactions. A goal is to time that the stimulus arrives at the subject. For improve gunshot timing estimates based on example, when a sound arrives at them or image observed film reactions and further inform and appears to them. In this case a gunshot sound correct some previous misconceptions along arrival time may be slightly after the shot was these lines. fired as the gunshot sound takes a little time to In situations where silent film or video reach the subjects depending on the subject-to- recorded during a crime is forensically evaluated gun distance. for evidence, it is common to assess the human In principle, an estimate of gunshot sound reactions visible to gain insight into the events arrival time to subjects for a surprise gunshot on that occurred. Identification of the type of silent film, as determined by observed voluntary reactions being displayed is important to help reactions, is obtained by subtracting a best put the scene in proper context and if timing of estimate of the general population’s median the stimuli causing reactions is to be estimated perception time after encountering a surprise for crime scene reconstruction purposes then stimulus from the median value of the sampled utilization of proper estimates on human onset times of surprise voluntary reactions reaction time is essential. observed for the subjects on film. The onset There have been examples in media over the time of these voluntary reactions indicates the past few years where the scope and interpretation end of a perception phase or perception time. of reactions and reaction time have not been A need for further promoting awareness presented clearly and in some cases have even on the subtleties of reaction time for use in been in error. In this study we re-emphasize analysis like this was recently highlighted while that voluntary reaction time is not just a fixed viewing documentary specials summarizing number, but in addition to the normal person- the assassination of the U.S. President John to-person variability in the population it can Fitzgerald Kennedy (JFK). Some forensic differ as a function of a number of factors assumptions in that case for individual and perhaps most commonly varies with the reactions and reaction times used to determine expectancy of the impending stimulus. the first shot timing in the shooting sequence Even though it has been known since Hirsch (a shot that missed), based on reviewing the that reaction time varies with the expectancy of Zapruder film, contained errors that continue

www.acsr.org 2 J Assoc Crime Scene Reconstr. 2020:24 to be referenced. These errors have resulted in any case when using a film or video format in a general consensus about the duration of is to get an accurate real-time full frame rate the shooting sequence and timing of the first, value which is necessary for detailed timing missed shot that is incorrect. calculations. The prevailing but incorrect timing estimate of the first shot in the Kennedy assassination Reactions and Reaction Time based off the Zapruder film is an understandable Material consequence of attempting to determine The material related to reactions and reaction the timing based on misclassified human time consists primarily of human factors reactions. Close inspection of and familiarity studies on involuntary (startle) and voluntary with reaction types are needed when reviewing reactions. human reactions in motion pictures where The following descriptions of flexion and interpretation can be challenging especially rotation will be useful herein for describing if the motion picture is low in visual quality, body movements related to joint articulations or silent, so that other contextual evidence is occurring in these reactions. limited or absent. The Zapruder film presents an Flexion: Bending the joint resulting in a excellent example to demonstrate how correct decrease of angle; e.g., moving the head forward application of reaction type and reaction time at the joint just below the skull. science can provide improved forensic estimates Rotation: Rotary movement around the on the chronology of surprise gunshot timing longitudinal axis of the bone; e.g., turning the occurring in silent films. head to the side (right or left) at a joint below Interpretation of reactions observed when the skull. analyzing silent film where gunshots occurred is likely to be increasingly useful in the future Characteristics of involuntary as video surveillance, police body cams, reactions of the startle reflex dash cams, and security cameras continue to Strauss [6] with Landis and Hunt in “The Startle proliferate (perhaps quasi-exponentially). Pattern” (1929) discusses using a revolver shot as a stimulus to isolate a definite startle behavior Materials pattern. It was a general flexion response, Material used to complete this research was symmetrical, and relatively uninfluenced by sourced extensively from published literature postural changes. and was gathered from two primary source Landis and Hunt [6] using pistol shots and areas: 1) for determinations of reaction time, high-speed photography, conducted similar published human factors studies on reactions tests which confirmed the Strauss results. and reaction times and 2) for the example Landis and Hunt noted the startle pattern to procedure, references on the Kennedy be rapid and involuntary, with the head moving assassination which described forensic analysis forward and down, along with other flexion using reactions and reaction time to determine motion, such as flexion of the fingers. a surprise first shot timing in that case. Carlsen [7] summarizes the literature on the Reaction time literature that shows how startle reflex in a thesis titled “Auditory Startle reaction time is a function of stimulus Response and Reaction Time” as a generalized expectedness is reviewed first. The literature was and diffuse protective response consisting of a found to contain reaction time data that can characteristic set of muscle actions initiated by be used in developing a perception time model a sudden intense stimulus. More specifically, for a surprise stimulus that is subsequently in response to a sudden, unexpected acoustic, applied to making estimates on stimulus arrival tactile or vestibular stimulus, a generalized time in our context. This summary is followed flexion response is observed in mammals. The by applying the perception time model to the startle response consists of a characteristic Kennedy case material. pattern of muscle flexion, as well as an increase It should be noted that although resources in central nervous system and autonomic including “film”, “motion pictures”, and activity. “video” can be technically different they can be Fetcho [8] describes the startle response as analyzed in a similar manner. Most important closing of the eyes and mouth, hunching of the

J Assoc Crime Scene Reconstr. 2020:24 3 www.acsr.org body, and contraction of the neck and torso Characteristics of voluntary reaction to protect vital body parts. “Startle responses time are rapid movements that occur very quickly Voluntary reaction time after a sensory stimulus following an abrupt, unexpected, strong sensory can be described as a combination of a cognitive stimulus, such as a loud sound produced by a mental processing time (i.e., perception time) slamming door. Startle or escape responses are and a subsequent voluntary movement time. shared by almost all animals, including both In traffic control studies Green [11] refers invertebrates and vertebrates. In many cases, to this combination as brake reaction time they are thought to serve protective functions where perception time (the mental processing such as avoiding the attack of predators.” time that it takes for a responder to perceive a The generalized flexion response of startle signal or stimulus and decide on a response), is has been hypothesized [9] to be an adaptive added to the subsequent movement time (MT) defense response in terrestrial mammals to it takes to perform the programmed movement. predatory attack from the rear, as the response In auto studies the movement time is the time results in reduced exposure of the dorsal surface required to move the foot from the accelerator of the neck, a vulnerable point of attack. Brown and engage the brake pedal. In equation form et al. [10] describe a similar response pattern it is: brake reaction time = perception time + consisting of eye closure, grimacing, as well as movement time. Brake reaction time is also neck, trunk, and limb flexion. commonly referred to as brake Perception- In contrast to the protective advantages of Reaction Time and likewise can be represented using neck/shoulder flexion motion, one could by: brake PRT = perception time + movement see how the startle reflex might not be a very time. effective instinctive evolutionary mechanism In the brake reaction time example for for protection if it relied on an involuntary voluntary reaction time, the time it takes to random left or right major head/neck rotation move the foot to engage a brake pedal once which exposes the front of the neck while that decision has been made is fairly quick and maladaptively putting the chin in a position programmed, on the order of a couple tenths of to block the protective raising of the shoulders a second, so that movement time is quick and needed to help protect the nape of the neck. We tends to have low variability. The perception can see, then, that head/neck rotation is unlikely time part of the voluntary reaction time is more to be a feature of the instinctive components of complex, however. the startle response. Human voluntary reaction time is a dynamic Startle is typically a rapid reaction consisting that can depend on a number of variables. of these quick flexion motions. It starts with Kosinski [12] conducted a literature review eye closing/blinking within ~100 ms followed on voluntary reaction time and studies which by more pronounced visible body movements looked at factors influencing reaction time. A that typically include head flexion forward/ number of factors have been studied including down and shoulders or arms rising up [6]. In variables like muscular exercise/arousal, fatigue, consumer quality video and films the more alcohol and drug use, illness, and muscle pronounced upper body motions are typically tremors. Many of these, however, could be observed about 200 to 300 ms after stimulus considered special case conditions. and subside quickly but reaction duration Like Hirsch, Kosinski points out a common can last a little longer with extremely intense variable that has been shown to be a highly stimuli. The general startle flexion movements significant factor on reaction time (RT): have been described as being similar to the “warning of impending stimuli” or “warning initial motions taken when beginning to move time” that a stimulus will occur soon. Kosinski’s into a protective fetal position. references showed that reaction times are Importantly, one key point of distinction faster when the subject has been warned that is that major head rotations are not flexion a stimulus will arrive soon, even when the motions and are not startle reactions. Major warning time preceding the stimulus is short. head rotations represent voluntary reactions. This variable has been shown to be fundamental relative to reaction time in a number of studies

www.acsr.org 4 J Assoc Crime Scene Reconstr. 2020:24 and can be classified by levels of stimulus consistent with a highly expected impending “expectedness.” Green [11], in studies on driver stimulus. Niemi et al. [15] state that the strength reaction time in automobiles calls expectedness of expectancy at any given moment during a the most important variable affecting voluntary trial determines the level of preparation to react reaction time when he says, “The most important at that moment, and that expectancy is flexible variable is driver expectation, which affects RT’s in that it can change rapidly. by a factor of 2.” Reaction time tests with mid- or in- Stimulus, reaction time, and between levels of expectedness to expectation in reaction time tests stimuli In voluntary reaction time tests, reaction time In order to further expand the amount of time is typically measured in conjunction with a elapsed between a preparatory warning and the movement time. For example, the end of brake occurrence of a reaction stimulus, thus increasing reaction time would be indicated by brake light the unexpectedness level, the range of studies was illumination when the foot movement first expanded to include lab and non-lab situations engages the brake, or in other research it might that included an office environment and outside include a hand moving to hit a switch or button driver reaction time studies in the auto industry that is used to time the total reaction time used in traffic flow theory. Reaction times of (perception time + movement time). drivers are important in highway design and To review the dependency of reaction time safe car operation. A number of reaction time on stimulus expectancy, and find appropriate studies involving stimulus expectedness along voluntary reaction time values for a complete these lines have been conducted. surprise, a broad range of reaction time studies Driver reaction time studies have added were examined. advantages in that they are not constrained An exact degree of expectedness is hard to to inside lab conditions, can effectively quantify, but it is reasonable to classify test incorporate much longer pre-awareness times, reaction stimulus into one of three expectedness and can produce reaction time estimates in groups, high/mid/low, i.e. a test will have some situations that are likely to be more reaction stimulus arrival expectancy at either representative than lab simulations of real life end of the expectedness spectrum or somewhere reaction situations. in-between. In this review we looked at high In this range of studies where the stimulus expectedness (where the stimulus arrival is was delayed after a notification or warning known to occur within a few seconds), low that a stimulus was coming at some point, expectedness (where stimulus arrival expectation so the expectedness was not extremely high, would be very low or totally unexpected), and the reaction times were noticeably longer. An awareness levels in between the extremes having effective warning of 32 s in one lab study [16], some mid-expectancy level. to within 10 m in a driver study [17], and even to a day or two in an office study [18], showed Reaction time in lab tests with a high median reaction times in these situations over level of expectedness to stimuli a range of about 450 ms to 800 ms. This group In studies by Luce [13] and Nickerson [14] could be categorized as a “mid-expectedness” that were conducted with a warning time situation. before stimulus in the range of 0.25 to 1 s, the Reaction time tests with low levels reaction times were in the range of 200 to 300 ms. This is similar to the reaction time range of expectedness to stimuli and seen in an internet human benchmarka reaction mathematical models time test where one reacts with a mouse click A few driver reaction time studies exist that to a computer screen signal a few seconds after focus on reaction time of unalerted drivers that starting the test. These reaction time tests are could qualify as a “low expectedness” situation. Taoka [19] noted that most reaction time experiments involved the testing of drivers who a https://www.humanbenchmark.com/tests/ were forewarned that their brake reaction times reactiontime

J Assoc Crime Scene Reconstr. 2020:24 5 www.acsr.org would be recorded and thus produced reaction the reaction time range summarized earlier time data taken under anticipatory conditions here for lab and driver studies with mid-level with values that were shorter than values expectedness. expected under normal real-life conditions. In Koppa’s paper he reported his mathema- Taoka goes on to say that the values that would tical models using brake reaction time (brake most closely resemble normal driving conditions PRT), since brake onset time was included. For are those that are measured for drivers who are our report, to get only the perception time, we unaware that they are being tested and who remove the chained or added on movement have not been alerted as to when braking will time parameter (in this case Perception time = be required. This would fall within our “low brake PRT – MT). expectedness” to reaction stimulus situation. Estimates on brake movement time are Taoka summarized four investigations which influenced by brake pedal separation relative looked at unalerted drivers and reported their to the accelerator pedal. Koppa found that if brake reaction time parametric values as follows: pedal separations were varied, holding the pedal size constant, the mean MT was 0.22 s. n=87, median=1.12 s, mean=1.14 s [20] A more recent study by Berman [26] showed n=839, median=1.14 s, mean=1.30 s [21] that by extending the displacement between n=579, median=1.10 s, mean=1.30 s [22] the accelerator pedal and brake by 45% the n=1644, median=1.07 s, mean=1.21 s [23] MT can be lengthened from the original 0.20 s value to 0.29 s. In a summary of reaction times Even with some differences in test design, Taoka by Yeomans [27], brake reaction time was also noted that in all four studies the corresponding reviewed with a range of foot brake movement measures of central tendency were generally in times from 0.17 to 0.3 s with a similarly reported close agreement. average of 0.2 s. We use 0.2 s as a representative Taoka’s overview of these 4 four studies mean value for brake MT from these studies to with real-life conditions of unalerted drivers estimate perception times by subtraction of this showed that the brake reaction times were fairly MT value from brake reaction times. consistent and notably longer than comparable Berman’s estimate on standard deviation for reaction time studies having higher impending her mean movement time of 0.20 s was 0.05 s. stimulus awareness. When considering removing the movement More recently, a literature review [24] time from the total brake PRT time we wanted included a summary of brake PRT (which to check if any reduction in standard deviation includes time to brake onset) from a wide for resultant perception time might be achieved. variety of studies. Based on sixteen studies Nonlinearly removing 0.05 s standard deviation from that review Koppa [25] created two from the standard deviation taken from brake mathematical models from the data as log- PRT did not have much effect on perception normal transformations for two types of time standard deviation so no reduction in response situations: (1) The driver does not standard deviation was claimed going from the know when or even if the stimulus for braking brake PRT model to the perception time model. will occur, i.e., they are surprised by something The perception time model we use is discussed like a real-world occurrence on the highway; further in the Methods section. and (2) the driver is aware that the signal to Overall, in lab studies and real-life driver brake will occur and the only question is when. studies the dependence of reaction time on Koppa’s mathematical model of the data for expectancy was seen throughout transition brake reaction time to a surprise stimulus gave from a high to low stimulus expectancy. This, brake reaction time having a median of 1.19 however, was expected and supports using s, a mean of 1.31 s, and standard deviation of extensive driver reaction time studies as a 0.61 s. This result was consistent with the four reliable basis for estimating the population’s low-awareness studies summarized by Taoka. perception time for highly unexpected or Koppa’s model for drivers with some surprise expectancy situations. awareness/expectedness gave brake reaction Additionally, beyond just a generally times having a median of 0.53 s and a mean observed increase in reaction time, the studies of 0.54 s. This result falls generally in line with that were reviewed show a fairly rapid rise in

www.acsr.org 6 J Assoc Crime Scene Reconstr. 2020:24 the magnitude of reaction time as the stimulus The erroneous reports about the first shot’s expectancy transitioned from highly expected timing resulted directly from misapplication of to totally unexpected/surprise. reaction time values to the observed reactions. The most critical error was mistaking voluntary Materials used to demonstrate human reactions for involuntary startle reactions manifested in the mistaken belief that the procedure for the Kennedy a startle reaction would involve major rotational assassination example motions of the head. This misconception can Materials on the Kennedy assassination still be seen in forensic analysis of the Kennedy consisted of government reports including the assassination to this day. Secondly there was a reports of the Warren Commission and the failure to account for the fact that the first shot House Select Committee on Assassinations was totally unexpected, i.e. a complete surprise (HSCA), books and journals on the legal event, which we know delays human voluntary and forensic aspects of the case, and digitized reaction time. versions of the Zapruder film. The premier piece of photographic evidence A number of books and journal articles used since 1963 to observe individual reactions have addressed the enigma known as “the lost to gunshots during the Kennedy assassination bullet” or “the first shot that missed” in the sequence has been the famous silent Zapruder Kennedy case. In some more recent work on film. the subject, DeRonja and Holland [28] recount Abraham Zapruder was a Dallas businessman that by 1979 investigations determined that who filmed the presidential motorcade as it the first shot fired was the one that missed, passed through Dealey Plaza on November 22, but left unanswered why that first shot missed. 1963. He used a Bell & Howell 8mm Zoomatic Motivated by some testimony that suggested camera that was filming at an average of about the shot was taken before the current consensus 18.3 frames per second. The Dealey Plaza timing estimate, they attempted to answer the filming consisted of 486 frames. The individual question on why the shot was a total miss and frames are commonly referred to with a Z proposed a possible deflection off a traffic mast prefix. Frames Z001 to 132 were taken before which would be consistent with a shot earlier the presidential limousine arrived in the plaza than current consensus. Nalli [29] reviewed on Elm Street and at Z132 Zapruder stopped some historic theories on the path the lost filming for a while until the limousine and bullet may have taken but mainly discusses that motorcade arrived. Frame Z133 is the frame the reason why the first shot missed may have where the camera re-started and Z133 to 486 been because of the shot’s difficulty in relation were the frames taken when the presidential to the target’s angular velocity. We believe that limo was passing down Elm Street in front of establishing an accurate chronology on the Zapruder. These frames (Z133 to 486) comprise timing of when the first shot happened can be Zapruder’s famous video segment taken at the extremely valuable in helping crystallize answers time of the assassination. to many of these shooting-related questions in The Zapruder film can be considered a clock the Kennedy case. of sorts during the assassination, ticking off at In this case for the first shot there were no ~18.3 frames/s. Since there was camera off time indications visible on film of the bullet striking for a while with no filming immediately before anything, so historic shot timing estimates Z133, in this report we will use a subscript eq have been based primarily on observing with a frame number for theoretical frames one individual’s (Governor John Connally) just before Z133 to represent an equivalent Z reactions attributed to the gunshot sound, frame number if the camera had been running then applying reaction time assumptions to continuously just before Z133. For example his movements. In the more than 55 years of Zeq115 would be a theoretical frame taken ~1 intensive analysis of the Kennedy assassination, second (18 frames) before the start of the actual however, the assumed basis used for the filming sequence that began at Z133. reactions and reaction time has been in error The evidence leading to the correct shot leading to a consensus about the probable timing is subtle: the Zapruder film is silent, timing of the missed first shot that is incorrect. yet evidence of the first shot’s early timing is

J Assoc Crime Scene Reconstr. 2020:24 7 www.acsr.org nonetheless unmistakable in the film upon described by the famous district attorney and careful inspection to identify voluntary prolific criminology author Vincent Bugliosi, reactions happening to a surprise external but at the time of his work, Bugliosi did not stimulus. have the perception time model discussed After identifying the reactions, it is important herein to aid in making a more accurate to identify the reaction type correctly. Errors analysis on the first shot’s timing. Even after in estimating when a first stimulus (gunshot its extensive review, the Warren Commission sound) arrived at individuals by back- was unsure on the exact first shot timing and calculating using a delay time can occur for two had reservations about assigning any Zapruder reasons: (1) mistakenly identifying the reaction frame for that shot, but Bugliosi espoused the type or expectancy level and/or (2) applying an prevailing consensus view as stated in his book incorrect associated delay time for the start of “Reclaiming History” [31] when he argued, the reactions. In the Zapruder film example, “However, there can hardly be any serious when back-calculating for the first shot, using doubt, despite the Warren Commission’s times for involuntary startle reactions (or reservation, that the first shot was fired around even voluntary reactions to a highly expected Z160 and missed the limousine.” stimulus like those seen at an internet reaction- Bugliosi additionally references the House time test site) will give an incorrect result; the Select Committee on Assassinations (HSCA) proper reaction type to use here is a voluntary investigation into the assassination, recounting reaction to a surprise stimulus. that “the HSCA, with a larger staff of scientific As seen in most Kennedy assassination experts, did closely examine this section of documentaries and books, the consensus first the Zapruder film. The committee concluded shot timing estimate in that case has been based that ‘the first shot…occurred at approximately primarily on early reactions of Governor John frame 160,’” and noted that this was “consistent Connally while he was seated in front of JFK with the testimony of Governor Connally, who in the presidential limo. Connally’s testimony stated that he heard the first shot and began to [30] was that he “heard this noise which I turn in response to it. His actions, as shown immediately took to be a rifle shot. I instinctively in Z162-167, reflect the start of a rapid head turned to my right,” and Connally can be seen movement from left to right.” turning his head right very rapidly early in In footnotes related to this issue, Bugliosi the Zapruder film as a concluding part of first asks, “If Governor Connally were reacting to the rapidly turning his head left. Unfortunately sound of a shot between Z162 and Z167, when this snippet of Connally’s testimony, along might that shot (with its contemporaneous with the rapidity of his head rotations seen on sound) have been fired?” Bugliosi goes on to film, has for years misled forensic investigators quote involuntary startle reaction times from into making the erroneous assumption that Landis and Hunt’s “The Startle Pattern” to Connally’s head turnings were an involuntary mistakenly back-calculate that “the sound of startle reaction to the first shot. Most forensic the shot would have been heard by Connally at evaluations have put the first shot around a about Z158-161.” quarter-second earlier than the concluding part To Bugliosi’s credit, even though the of Connally’s head turns (the concluding right reactions were misidentified as startle, he did head turn by Connally is seen at Z162 to 165), or recognize some limitations in the state of forensic the equivalent of about 5 Zapruder film frames reaction time analysis when he speculated that based on typical 250 ms startle reactions from a it might be possible that for some individuals loud stimulus like a gunshot. The predominant the startle reaction time could be longer than consensus first shot timing estimate in this case near instantaneous. He hypothesized that if has been placed around Z157 to 160 based this were true, it might be possible for the shot primarily on Connally’s reactions to the first to have occurred as early as Z140. shot, misinterpreted by investigators as a startle The clear giveaway that the historically mis- reaction. characterized rightwards head turn by John In one of the more comprehensive reviews of Connally was in fact not a startle reaction is this case which included a first shot analysis, the exaggerated rotational nature of Connally’s crime scene reconstruction details were head movements. Those major left, then right,

www.acsr.org 8 J Assoc Crime Scene Reconstr. 2020:24 head rotations are each grossly non-symmetric have skew (like those seen with reaction time relative to the sagittal plane and consist of very distributions), the median value is commonly large rotation motions of the joints of the neck. considered the preferred statistical measure of Likewise, all other reactionary head rotations central tendency to use instead of the mean or by persons other than Connally observed in the mode. We use the median statistic as the the Zapruder film are not involuntary startle measure of central tendency to align with. reactions, but rather voluntary or secondary After reviewing a film and its context the reaction movements of rotation. The appropriate general procedure for the analysis entails the indicated action to consider when using the following steps: start of head rotations to estimate shot timing is not based on startle reaction time but rather 1. Assess whether or not any gunshots that occur voluntary reaction time and specifically, for the during the suspected point on the film would unexpected first shot, the perception time after have been be a surprise (in that there would arrival of a surprise stimulus. not have been much expectancy for gunshots It should be noted that the more recent at that point), and that individual reactions advent of personal computers, digitized film, are visible enough to be identified by type. newer reaction time studies, and the Internet are resources that early investigators did not 2. Conduct a close inspection of the individuals have at the time. These tools greatly facilitate visible on film around the time of interest to access to information and evaluation of forensic identify any first signs of voluntary reactions evidence for crime scene reconstruction and to a surprise stimulus. If possible, evaluate the have played a key role in the development of film in both a frame-by-frame context as well this report. as in a continuous running mode.

Methods In this context the start of surprise voluntary The method developed to help estimate silent reactions will be different from either startle film surprise gunshot sound arrival timing is reactions or commonplace voluntary reactions based on identifying the subject’s perception (such as, casual head-turning or looking for a time, as indicated by the beginning of non-urgent reason) and will include upper body voluntary reaction movements observed on twisting or leaning and/or head rotations left film consistent with reacting to the surprise or right in a classic “what the heck was that?” stimulus. Involuntary startle reactions could reaction used for sound localization and visual be considered separately as supporting data field expansion in order to determine what but because startle reactions can be very short just happened. Some judgment in context is in duration and small in magnitude they may necessary, but unusual twisting, bending to be hard to observe in videos that are filmed at the side, atypically rapid head movement or a distance, at low resolution, or in low light. accelerated motion left or right, or related As such, to get at the stimulus arrival time, concerned or urgent looking motions including the method focuses on sampling individuals’ distinct changes in facial expressions would all beginning of voluntary movements (the be indicative. Observed reactions should be beginning of a movement time) consistent with noted to begin when a position change is the reacting to gunshot sound which equates to first in a series of sequential frame-to-frame their perception time after the arrival of the changes that are consistent with a progression gunshot sound stimulus. The method then of these reactive-type motions. These beginning aligns the best measure of central tendency for movements represent the end of perception the sampled perception time data to the best time (i.e., latency) after a stimulus, and the available central tendency value for perception beginning of movement time and a movement time of the population as a whole in order to response. If there is real uncertainty on the back-calculate a stimulus time 0, the gunshot identification of the reason for any individual’s sound arrival time. reactions, it is suggested to hold off and not use Although the mean is a typical statistic to use that individual as a sample. for assessing central tendency on distributions having continuous data, for distributions that

J Assoc Crime Scene Reconstr. 2020:24 9 www.acsr.org 3. Note a reference time or frame number for for brake PRT employed a standard response the start of the observed reactions for each log-normal probability density function. individual who is showing signs of reacting as Generating a related model for perception identified in step 2. time by removing the brake movement time parameter from brake PRT, we get a similar Ideally one might see and use multiple log-normal perception time probability density individuals having reactions happening around function estimate for the population having the the same time on the film (surprise reactions of following format: multiple persons should occur within a second or two time span of each other if they are reacting to the same stimulus). Record all the (1) observable starts of surprise voluntary reactions relative to a film/video reference frame or reference time. It should be noted that not where t is perception time, λ= -0.028 and everyone in a population will show observable ξ=0.514 are model constants, and f(t) is the reactions to a given stimulus. associated equation for the probability density function. For this surprise stimulus situation 4. After all sampling of individual reactions is without brake movement time the modeled complete, calculate the median time value perception time median value is 0.97 s, the for the beginning of voluntary reactions of all mean value is 1.11 s, and standard deviation the individuals observed, then subtract the is 0.61 s. Given the number of studies used in best available median voluntary perception Koppa’s modeling, this approach should provide time to a surprise stimulus for the general a good representation for the distribution of the population (subtract the known population general population’s real-life perception time to median value appropriately using the same a surprise stimulus. units as the sampled data, i.e. a time value or A graph for this perception time function is number of frames). The resultant value will found as the top graph depicted in Figure 1 where be an estimate of initial gunshot sound arrival the y-axis is the perception time probability time to the individuals on the film under density function for a surprise stimulus and the consideration. x-axis is perception time in seconds. The probability density function shape here If there are multiple observations of voluntary can be thought of as a graph of the relative start-of-reactions, then it might be beneficial to likelihood that an individual in the population compare their distribution to that of the general would have a given perception time. The curve population. This could be used as supporting shape will mirror the shape of a sampling evidence that the samples selected were all histogram from the population as the histogram results of the same stimulus. Optionally, grows, filling in upward and outward as more plotting a histogram of the sampled data perception times sampled from the population centered (using the median) against a plot of the are added. expected frequency of perception times found in the general population may help as a visual Checking the model and potential reassurance on the quality of sampled data. impact of two associated Identifying a base mathematical parameters model to use for the general The model we employ based on Koppa’s approach of using empirical data from studies population’s voluntary perception with surprise reactions should provide a good time for a surprise stimulus representation for perception time, but it was The model used here for perception time for a decided that it would be worthwhile to do a complete surprise stimulus was developed based quick check in our context and additionally on Koppa’s brake PRT modeling approach to a review a couple of associated reaction time surprise stimulus. Derived from extensive auto related variables that might come into play driver studies, Koppa’s mathematical model and assess if they would have an impact on the

www.acsr.org 10 J Assoc Crime Scene Reconstr. 2020:24 1.0

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126 128 130 132 134 136 138 140 142 144 146 148 150 152 154 156 158 160 162 164 166 168 170 172 174 176 178 180 182 184 186

Film restarts at Z133 Zapruder Frame

Figure 1: Composite of two graphs including an estimated population probability density function of perception time for a “surprise” stimulus vs. perception time in seconds (top), and a histogram (1/2 frame bin width) of early observed voluntary reactions in the Zapruder film vs frame observed (bottom). Frame numbers before Z133 represent equivalent frames had the film run continuously before Z133. utility of using the perception time model to ~50 ms faster than visual reaction time [3]. estimate surprise audible gunshot sound timing Likewise, Nickerson [14] describes experiments on silent film/video. The other two variables where reaction time was about 50 ms shorter that were considered worth reviewing are 1) on the average for auditory stimulus versus auditory stimulus vs visual stimulus in reaction visual stimulus. The studies reviewed indicated time dynamics and 2) effect of loud stimuli and a slightly smaller reaction time for auditory vs startle on voluntary reaction time. visual stimulus in lab tests. Dynamics of auditory vs visual Effect of loud stimuli and startle on stimulus related to reaction time voluntary reaction time A composite of reaction time studies was the The effect of loud stimuli is dependent on basis used to generate our surprise stimulus a number of stimuli factors. Responding to perception time model and these, as well as auditory stimuli can depend on frequency and possible future studies that might augment duration, but especially on loudness level. A the work, include a mix of driver reaction time brief survey here can give some perspective on research that utilizes auditory stimulus (like a intensity effects, with the A.M. Brown et al. horn) and/or a visual stimulus (like onset of a report [32] being especially relevant given their bright light flashing or a road hazard quickly testing with a gunshot sound. appearing). It is worth seeing if there is any Niemi et al. [15] presented a summary graph meaningful difference in reaction time for on auditory and visual simple reaction time as auditory versus visual stimuli relative to the a function of reaction stimulus intensity. Both overall reaction time values as research studies auditory and visual reaction stimuli, when can include either approach. Using this paper’s presented at greater intensity, elicited slightly technique for estimating occult (i.e., “hidden” lower reaction times versus when presented at or difficult to discern) gunshot timing from lower intensities. For example, in the auditory silent film we would expect the reaction case the strong vs weak intensity RT difference stimulus to be a gunshot sound (auditory was about 20 ms and in the visual case the stimulus) rather than, say, a gunshot muzzle strong vs. weak intensity RT difference was flash (visual stimulus) that might not be seen on about 25 ms. film yet was visible to the subjects. Given that Brown et al. [32] used a recorded starter-gun visual stimulus is not uncommon in research it gunshot for a sprinter race simulation to test is worth having a look at differential times for the effect of loud sounds and startle on reaction auditory and visual stimuli. time. From 80 to 100 dB there was a decrease Early testing by Hirsch in the 19th century in reaction time of 10 ms. When looking at indicated that auditory reaction time was startle effect, they found a similar reduction in

J Assoc Crime Scene Reconstr. 2020:24 11 www.acsr.org reaction time of 18 ms at 120 dB when a startle utilizing about 15 frames per second, video occurred. frame-to-frame change time is about 0.067 s. In a test with an increase in a sound intensity A difference in an individual reaction time that similar to that in Brown et al., Nickerson [14] is less than this effective one-frame change time reports graph data from [33] with a reduction likewise is not considered to be a meaningful in reaction time of ~15 ms when increasing difference for this analysis. intensity of an auditory stimulus from 80 to 100 dB. Checking the model in our context Inspection of these tests suggests that there is a small relationship between stimulus intensity using video containing a known and reaction time. In these auditory tests across loud/surprising stimulus the range of 80 to 100 dB, but below startle As a quick check on the perception time evoking sound intensity, a corresponding model in our context with data that included reduction in reaction time was seen ranging a startle reaction, a related control evaluation from about 10 to 20 ms. Startle effect (typically was conducted. This check was compiled commencing at ~120 dB) likewise had similar from random sampled videos that included effect on reaction time of 18 ms. individuals reacting to a surprise auditory If a loudness impact and startle are combined stimulus and which additionally included an it would still appear to have a small effect on initial startle as part of their overall voluntary reaction time of less than 50 ms (36 ms was reaction sequence. The videos used in this seen in the Brown et al. study using gunfire assessment were not chosen from silent film sound). but from video with recorded audio so the Thackray [34] commented along these exact time of the auditory stimulus was clearly lines in regard to total response time when he evident and could serve as a known control on concluded that simple, voluntary responses the timing of the sound arrival. to startling stimuli or events generally occur Reaction time sampling was obtained from within 1 to 3 s following stimulation. In this five videos chosen at random from internet regard, mean time to respond to a startling discussions where they were presented by stimulus may not differ appreciably from mean researchers as video examples showing startle time to respond to an unexpected event or reactions. The videos appeared to be of high stimulus that is simply surprising. enough quality so accurate tabulations on In the brake PRT literature reviewed, visual reactions and reaction times could be made. and auditory stimulus intensity were not The procedure used for reaction time evaluation specific dependent variables modeled, and a mix was the method described earlier herein while of these variables was used in the compositing looking for characteristic involuntary startle of the studies used to create an overall brake and voluntary reactions. The videos were loaded PRT model, but it would appear a specific into software that indicated video frame time visual or auditory stimulus incident would not and allowed for full speed running as well as introduce a sampling reaction time error of frame-by-frame evaluations in order to identify more than about 50 ms compared to the brake the start of startle reactions along with the PRT reference model. We believe this amount subsequent start of the voluntary reactions. is not enough to impact the utility of the sound Reaction time starts in each film were measured arrival time estimates for surprise events based from the recorded surprise loud audible stimulus on the models. which was referenced as time 0. The recording For perspective, if there was a maximum video microphones appeared to be close to the 0.05 s time difference in individuals’ reaction individuals showing reactions, so sound arrival or perception for a particular case due to the to the mic and subjects was assessed as being stimulus, then relative to surprise reaction time effectively simultaneous. In videos where there data used to derive the model it would represent were multiple individuals showing reactions, a difference of <5% of the main variable of sampling was limited to two samples in order interest (median perception time of around 1 to help maintain overall sampling randomness s). Additionally, with the expected use of this where no one film would overly represent technique on standard surveillance videos voluntary reactions. This sampling process

www.acsr.org 12 J Assoc Crime Scene Reconstr. 2020:24 netted seven voluntary reaction samples taken Method exemplified as applied to from five different videos (7 samples is the the silent Zapruder film count taken from the Zapruder film example As mentioned earlier, not all individuals on as well). film will show visible reaction to stimulus, A list tabulating the starting time of but typically after a given surprise external observed startle reactions and associated stimulus, there will be observed a start of voluntary reactions is found in the upper half of asymmetric, atypical, or unusual individual Table 1. Descriptive statistics for the sampling voluntary reaction movements on film (which are summarized in the lower half of Table 1. are not involuntary startle reflex movements) The descriptive statistics calculations were that will signify the end of perception time and performed using Microsoft Excel. the beginning of subsequent voluntary reaction The mean and median observed starts of movements in response to the surprise stimulus startle reactions (234 ms, 200 ms) are in close and represents the beginning of MT. agreement with literature values seen for startle, Keeping the characteristics of the reactions and additionally within the seven samples taken in mind, close inspection of the early parts on start of voluntary reactions there was rapid of the Zapruder film while it was tracking convergence of the video samples’ median value President Kennedy’s limousine was conducted (0.95 s) to the perception time model predicted to identify the start of any urgent-looking or median value for a surprise stimulus (0.97 s). unusual voluntary actions for individuals in These results provided additional reassurance the motorcade that were consistent with being that the perception time model is a good voluntary reactions to a notable and surprising estimator for the population’s start of surprise external stimulus from the first shot. voluntary reactions in a general case even if a The authors independently observed and brief startle is included. compiled a list of representative early voluntary reactions for individuals in the presidential

Table 1: Author observation times for start of reactions after a surprise auditory stimulus. Taken from 5 random videos where a surprising loud audio sound causing startle occurred.

Observed Observed start of Video Sampleda start of Startle Voluntary reactions (ms) reactions (ms) Girl startled by loud 270 940 sound from behind Basketball explodes 200 800 & 950 on playground (2 individuals sampled) Man gets a startle when 200 1300 balloon pops Polish Soldiers surprised 300 800 & 1270 by a shot (2 individuals sampled) Basketball Coach reacts 200 2000 to fireworks Sampling Descriptive Statistics Median (ms) 200 950 Mean (ms) 234 1151 Standard Deviation 47.75 425.93 Sample Variance 2280 181414 Count 5 7

a https://sites.google.com/view/sampled-startle-and-voluntary-/ home

J Assoc Crime Scene Reconstr. 2020:24 13 www.acsr.org limousine and the trailing Secret Service limo. In this case sound localization for a first quick, All of these early reactions observed on film albeit loud, noise located behind and high happened in close time proximity (all were overhead would likely be much more difficult within just over half a second of each other). Both than ground level localization of sounds at authors used the same method to determine the either side or in front, and would have made start of these voluntary reactions. Combining it more difficult for some individuals, based the authors’ data for each individual in the film only on a brief completely unexpected first who was observed led to one data point for each shot, to localize the sound source and decide individual to be used in the final evaluation. which way to look. Although speculative, these Trying to catch the first frame for a start reasons might help explain some variations in of reaction (start of movement time after the the observed voluntary reactions. stimulus has arrived and perception time is An additional note here is related to the complete) on a moving film can be challenging, Zapruder film rate and our analysis. As so the method suggests loading the sequential mentioned, the FBI conducted a rigorous digitized frames from a film into viewing analysis and determined an average overall software that enables stepping frame to frame frame rate during use to be 18.3 frames/s. and back again and zooming in as needed. The inverse of this is 0.055 s/frame. The Bell The digitized Zapruder frames used in this & Howell 8mm movie camera used 1/40 s or case are publicly available on the internet.b The the equivalent of 0.025 s for film exposure. beginning and early part of the film sequence This means there would be a duration of about on Elm Street (frame Z133 to about frame 0.03 s where no exposure was occurring during Z165) were inspected closely for any indication each frame cycle (the time needed to advance of urgent-looking or unusual voluntary the exposed film out and move new film in movements like twisting, bending, atypically position for the next frame exposure). As rapid head movements or accelerated motion such, film exposure was not continuous, and left or right. Observed reactions were noted to during roughly half of the frame cycle time no begin when a position change was the first in a exposure was occurring. So if a visual photo series of sequential changes that were consistent frame number is referenced, that is the image with voluntary reactive-type movements. captured in about the first half of that frame Only individuals that displayed clear cycle. When calculations are done using frame voluntary reaction type movements were numbers there can be fractions of frame values sampled. For some of the individuals visible that come up. For example, frame Z143 and in the Zapruder film it appeared there might Z144 could average to Z143.5. We use tenths of be some motion of worried reaction, but frames to demarcate a continuous timeline for the quality of the film made it difficult to be the entire frame cycle and as a way to be able certain. These were not included. It should also to align the Zapruder film with a continuous be noted that some individuals did not appear clock. In practice we just interpret any frame to react at all or the reaction was too small to number having greater than a 0.5 fraction as observe. Lack of reactions may seem a little representing a frame time in the second half of unusual given that a gunshot had just occurred its total frame cycle which could be considered but is consistent with comments made by as a time during filming that is between Koppa in his report where some subjects appear individual frame exposures. oblivious to a stimulus. Koppa did not elaborate why, but a possibility for some bystanders in this case was that the intensity of their focus Results (Applied to the Zapruder on the presidential limo right in front of them film) commanded their attention more than a first As mentioned earlier, examining the Zapruder background bang sound, and for some of the film sequentially frame by frame is preferred motorcade occupants turning to check out for identifying the start of individual voluntary a noise would depend on the direction one gunshot-sound reactions, but viewing the thought the noise source might have originated. film in motion can also provide perspective on seeing these multiple reactions (by several b http://www.assassinationresearch.com/zfilm/ people) happening at about the same time.

www.acsr.org 14 J Assoc Crime Scene Reconstr. 2020:24 Positioning for the individuals observed having model median perception time of the general early urgent-appearing reactions and zoomed in population for a surprise stimulus (0.97 s segments of the Zapruder film at normal and median, converted to a number of Zapruder then reduced speed can be seen online at an frames) and subtracting that from our sampled Early Zapruder Film Reactionsc webpage. overall median frame for the start of the A listing of the associated starting frame of early reactions observed in the Zapruder film the reactions as tabulated by each author and (Z143.5). our average start of reaction frame for each First shot sound arrival timing estimate individual is found in the upper section of = frame Z143.5 – (0.97 s) × (18.3 frames/s) =

Table 2. frame Zeq125.7 It should be noted that reactions tabulated This result can be seen visually when looking from a film of interest need only be done by one at Figure 1 with a classic slide rule operation in film examiner but for this analysis, as listed in mind. On the top graph put the cursor line on Table 2, the start of reaction frame used herein the general population’s median value for the for an individual is the average of the two surprise perception time distribution (0.97 s). authors’ sampling observations. This was done Then slide the bottom Zapruder film frame because the authors independently conducted scale left or right in order to line up the overall reaction assessments, but the data was averaged median of the early film observed start of in order to report just one result. The two reactions (Z143.5) with the cursor line. Finding authors’ measurements were in close agreement, time zero (the stimulus arrival time) on the top though, as estimates were within about a frame perception time graph, read below that zero of the individual respective means. point to the equivalent point on the Zapruder

The overall start of reactions-descriptive frame scale (Zeq125.7). statistics are summarized in the lower section To estimate sampling error around the of Table 2. true median of start of reactions and assign Based on the surprise perception time model a 95% confidence interval range, we use for the population in Figure 1, we would expect the knowledge that the data is lognormally a number of voluntary reactions to appear in the distributed. Given this we transformed the data vicinity of the 0.97 s median perception time by taking the natural log of the raw data using value, between 0.70 and 1.3 s after a surprise the ln(x) function, which normalizes the data, stimulus, i.e. within a time interval window of before calculating a Standard Error statistic. ~0.6 s. Notably, this closely matches the time The transformed median becomes the mean range in which the individual early reactions estimate of the transformed data. The timing were observed in the Zapruder film, between uncertainty is obtained in the transformed Z140 and Z150, which was 0.55 s. domain by Mean + 1.96 × (Standard Error). A histogram of the authors’ start-of-reaction This interval is then de-transformed back to frames for the individuals sampled and the regular frame data using the ex function. In the overall median frame value of the individuals transformed domain the data mean was 4.9745 (Z143.5) can be seen added to the top graph in and the standard error 0.0087. the composite graph of Figure 1. The *’s in the This procedure yields a confidence interval figure are the start of reaction frames for the around the start of reactions median value individuals plotted above the perception time (Z143.5 target) of ~Z142.2 to Z147.2. The range axis, which is scaled to match the Zapruder asymmetry around the median target value is a frame axis (in frames) below it using an average consequence of the skew in the distribution. film rate of 18.3 frames/s. As depicted earlier, subtracting the population model median value of 0.97 s Arrival timing estimate for the first (or 17.8 frames using a camera rate of 18.3 shot sound frames/s) from our sampled start of reactions The arrival timing of the first shot sound target and range points gives us estimates on is estimated by taking the mathematical the target value and range for the sound arrival

at the limo. In this case it’s a target of Zeq125.7 c https://sites.google.com/site/earlyzapruder and a range from ~Zeq124.5 to Zeq129.4. filmreactions/reactions-seen-early-in-zapruder-film Estimating the presidential limo position at

J Assoc Crime Scene Reconstr. 2020:24 15 www.acsr.org Table 2: Individuals observed having apparent voluntary reactions to an external stimulus about the same time in the early Zapruder film and observed start of reaction frame number by author. Average start of reaction by individual on film and overall Median start of reactions are indicated.

Individual showing Author-a Author-b Avg. of Comments noticeable observed start observed start Authors’ early reactions on of reaction of reaction values (used film frame frame in analysis/ stats†) Roy Kellerman 148 148 148 Begins leaning over and looking behind/down to the right

George Hickey 144 143 143.5 Begins leaning over to the left looking down in the direction of the rear tire or ground John Connally 151 149 150 Begins a quick head turn left (followed by quickly looking back right) Jackie Kennedy 145 142 143.5 Starts accelerated head turning left, before looking back right. (Similar to John Connally’s L-R head motion but starts slightly earlier & ends slightly later than his) President Kennedy 144 142 143 Starts a quick look to the left Nellie Connally 146 144 145 Begins a quick sweeping head turn to the right Rosemary Willis 141 139 140 Begins a quick look away from the Presidential limo back towards the Texas School Book Depository † Descriptive Statistics Statistics conducted on the (N=7) average of authors’ values reported for each individual Median 143.5 Standard 3.34 Deviation Mean 144.7 Variance 11.15

the time its occupants would have heard the delay in frames from our limo sound arrival

gunshot sound at around Zeq125.7 and applying timing estimates gives an estimated trigger

Google Earth Pro, the calculated direct line time target value of Zeq124.0 with a range from

of sight distance from the sniper’s nest to ~Z eq122.7 to Zeq127.7.

the President would have been ~107 ft [32.6 An estimate of frame Zeq125.7 for the gunshot m]. Using 1123 ft/s [342.3 m/s] as the speed sound arrival time has the first shot sound of sound and 2165 ft/s [659.9 m/s] as a value arriving at the limo a little under half a second for the initial velocity of the Carcano bullet before Zapruder restarted his camera at Z133. and neglecting (as negligible) its slowdown Allowing for the first shot to have originated on a trajectory directed towards the limo, we from the Texas School Book Depository sniper’s estimate a sound delay from the trigger time to nest and the sound travel time from there, it its limo arrival. Trigger time estimate = Sound translates to a gunshot origination time (trigger

arrival at limo time estimate – sound delay in time) estimate of about Zeq124.0. Given that a traveling from the rifle to limo. final shot was taken from the sniper’s nest just In this case the sound delay is estimated at before Z313 the entire shooting sequence took ~0.095 s or ~1.74 frames. Subtracting this time about 10.2 s.

www.acsr.org 16 J Assoc Crime Scene Reconstr. 2020:24 The Zeq124 trigger time estimate assumes Review & Conclusions that a supersonic shock wave did not arrive at The model for estimating gunshot timing on the limo far enough in advance of the muzzle film based on voluntary reactions was developed blast to cause the early voluntary reactions. We from data taken from extensive driver reaction would be confident that this did not happen time studies in automobiles related to traffic if the lag time between a Carcano rifle bullet flow theory. Since this model was based on arriving at or passing close by the limo subjects multiple studies measuring reactions to a (as the tip of a cone shaped shock wave) and surprise stimulus, the expectation is that this the following muzzle blast sound, was similar is a robust basis for the method employed to or less than the delay time it typically herein to make surprise gunshot-sound timing takes for individuals to discern two sounds as estimates. separate sounds. This dynamic is related to the Although the model has an empirical basis, precedence effect in sound localization when a a check was conducted by sampling some films sound is followed by another sound separated by (having audio) containing a surprise auditory a sufficiently short time delay that the listeners stimulus and subjects showing brief startle. perceive a single or fused auditory event. This is This evaluation was used as a type of control to a fairly complex dynamic and depends on the check against the model. The resultant median testing but studies indicate that listeners can perception time of the control data closely continue to experience a fused auditory event matched the model. In addition, the sampling when the lag time is up to ~50 to 80 ms [35, distribution of the control data generally 36]. paralleled the shape of the sampling distribution Using the limo distance estimate from the trend for the population model as did the sniper’s nest along with velocities of the bullet Zapruder data. This can be seen by plotting and sound applied in the calculations above, the voluntary perception time data from the we can estimate a maximum sound lag time films containing audio with the Zapruder film at the presidential limo of ~46 ms. Given that data whose median is set alongside the model a 46 ms delay is in the range where we would median value. That plot is found in Figure 3. expect auditory fusion, for this scenario if there The sampled individual data points from the was a shock wave based on the bullet trajectory, Zapruder film plotted together with the other the limo subjects would not discern separate random videos sampled for voluntary perception shock wave and muzzle blast sound events. time appear to show an overall histogram This indicates that the assumption of using building in a log-normal form as expected, and the muzzle blast (or fused muzzle blast) as the with more extensive sampling should further surprising sound they heard is reasonable. match/mirror the distribution shape of the continuous perception time probability density An intermediate perspective function of the mathematical model. The first shot timing estimate using this new In detailing these procedures for gunshot technique seems to provide an intermediate timing estimation, the Zapruder film was chosen estimate compared to previous hypotheses. as a silent film that captured an event with One scenario involving the traffic mast has surprise gunshots and contemporaneous visible the timing at about 17 to 18 frames earlier voluntary reactions and provides an excellent than our estimate and another very common example of leveraging voluntary perception “consensus” hypothesis discussed earlier, that time as a function of expectedness to determine may have involved oak tree branches, has the the timing of a surprise gunshot where other shot taken about 30 to 36 frames later. evidence of the timing is unavailable, because For a visual perspective on these shot the film is silent and no bullet-strike evidence positionings, Figure 2 presents frame grabs from is available. Applying the procedures to the a 1963 Secret Service reenactment video filmed Zapruder film was fairly straightforward and from the sniper’s nest. These frames depict the provided new insight into the timing of the first 3 different first shot timing points and include shot in the Kennedy shooting. the approximate limo location at its equivalent The procedure presented here is independent shot frame as depicted by the stand-in limo. of using any recalled testimony but rather uses

J Assoc Crime Scene Reconstr. 2020:24 17 www.acsr.org Figure 2: Frame grabs from the Secret Service reconstruction film depicting the view from the sniper’s nest for

this paper’s estimated shot trigger time (middle picture at ~ Zeq124) compared to two previous hypotheses. The red box around the stand-in limo indicates a 95% confidence interval for our shot timing/limo position using this video.

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126 128 130 132 134 136 138 140 142 144 146 148 150 152 154 156 158 160 162 164 166 168 170 172 174 176 178 180 182 184 186

Film restarts at Z133 Zapruder Frame

Figure 3: Plot of start of early Zapruder film voluntary reactions observed (red *’s) and data sampled from random video containing voluntary reactions to a surprising audio stimulus (green +’s with median=0.95 s). For this reference both data sets are combined as a histogram plotted below the shape of the surprise stimulus perception time model probability density graph. The median of the Zapruder film data in this 27.3 ms bin width histogram is set alongside the cursor centered on the mathematical model median of 0.97 s. reaction time science applied to observations with film inspection or reaction types before of surprise voluntary reactions seen on film. In the data is, or is not, used in this context. the case of John Connally along with the other Another factor to consider is that the individuals sampled on the Zapruder film, this confidence level/accuracy of a gunshot timing technique should provide a reliable estimate for estimate is dependent on the number of data the timing of the surprising first shot in that points (number of subjects with observable case. voluntary reactions) showing appropriate reactions on film. When sampling from film to Limitations estimate the median start of voluntary reactions, The most significant limitation in applying this using multiple data points (if possible) will help method to estimating gunshot timing is that provide a better estimation on the gunshot the reactions observed on film are voluntary sound arrival time. In situations where only reactions of surprise and as described in the text one individual can be observed, higher gunshot those reactions have to be correctly determined sound arrival time uncertainty exists because to be reactions of concern; incidental random of the natural individual variation within the or non-urgent causes for observed movements population on surprise voluntary reaction time, should be ruled out. To be surprising, one has to so awareness of this limitation is called for when judge by the context of the film that there would using arrival time estimates in those cases. not have been much expectancy for gunshots. A related time we refer to is the gunshot For the most part this will limit gunshot timing origination time, which is before the gunshot estimation to the first shot that happens in a sound arrival time, and is when the gunshot shooting event sequence as subsequent shots originated. This can also be referred to as have in effect been forewarned by earlier shots the “trigger time”. In some cases involving a and expectedness can change rapidly when surprising gunshot, investigators may want an aided by a strong forewarning stimulus. estimate on the gunshot origination time or When conducting rigorous review of all trigger time, but as described in the text this the evidence in a case which includes film to technique’s output is an estimate on gunshot inspect, the film used should be clear enough sound arrival time for the individuals evaluated to make a judgment on when and what type on film. An estimate on gunshot sound of reactions are being observed. If there is any arrival time might be a limitation in some concern about being able to make a correct circumstances, but in many situations it may be identification on the type or timing of reactions possible to further make an estimate on trigger being observed, it might be helpful to look for time by using arrival time if investigators can assistance from an expert or others familiar make a determination on where the gun was

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