8. the Timing of Death

8. The Timing of Death Benjamin Swift Introduction Death is inevitable, although it occurrence is unpredictable. Decedents are often discovered at intervals of variable length after the actual event, depending upon the mode of death and the location of death and social factors, such as the geographical and psychological proximity of relatives. Despite the almost supernatural abilities of fictional pathologists, the capacity to estimate the time of death remains limited in forensic practice. In the absence of documentary evidence of fatal collapse, such as closed-circuit television surveillance footage, investigators must rely upon addi- tional information derived from three main sources: D Evidence provided by the body itself, D Environmental and artifact-based evidence, which is evidence in association with a body, and D Anamnestic evidence, which is based upon the knowledge of the individual’s movements and day-to-day activities.1 Although the majority of police investigations rely upon the latter two sources, the literature is constantly expanded by methods extolling the vast number of iden- tifiable alterations that may occur during the postmortem interval (PMI), to which a temporal value for the time since death can be ascribed. Requirement for a Dating System “When did they die?” continues to be one of the major questions during a death investigation and is one of the main questions posed during an inquest into the fatal events presided over by Her Majesty’s Coroner.2 Therefore the chronologic dating of events is of great importance to forensic investigators (as with ancillary scientific studies such as geology and archaeology), that is, the ability to create a theoretical timeline upon which the social interactions and events of a person’s last days assists in either eliminating or incriminating others from an inquiry. Of the methods published, the majority can be divided into two main categories: those occurring within the early postmortem period and those during the late 189 190 Essentials of Autopsy Practice postmortem period. The arbitrarily defined early postmortem period relates to the soft tissue phase of decomposition, whereas the late period refers to the phase of skeletalization and subsequent taphonomic alterations to the bony matrix itself. Early Postmortem Interval The literature relating to PMI estimation within the soft tissue phase of decomposition is extensive, being constantly updated each year with novel or adapted tech- niques. Although it is not practical to discuss all methodologies within this chapter, reference is made to dedicated texts where in-depth information can be found.3 Algor Mortis Algor mortis relates to the postmortem cooling of a body and relies upon the knowledge of a steady-state core body temperature during the antemortem period, presumed to be approximately 37°C. Davey’s experimentations with cadavers in 1839 resulted in one of the first scientific investigations into the issues of dating time since death.4 The basis lay in Newton’s Law of Cooling, which states that for a body cooling by forced convection the rate of heat loss is proportional to the differences in temperatures between the body and its surroundings. This law, however, is applicable only to regular inorganic spherical objects. Although it formed the basis for much early research, the law fails to account for the irregularity of the human form, the effects of clothing, ventilation, or physical positioning of the cadaver. In fact, during Davey’s study while in British-occupied Malta, the high ambient temperature frequently resulted in the temperature initially rising in cadavers during the early postmortem period. The anatomical sites from which temperature readings are taken vary, the prin- cipal locations being the brain, skin surface, nasal cavity, axillae, rectum, and individual internal organs, as cooling occurs at different rates for each site.3 Given the variables relating to the human body, experimentation has confirmed that Newton’s law fails to hold. Rainy first described a recognizable anomaly in 1868, referred to as the lag phase or plateau.5 Rather than the expected single exponential curve of temperature loss, a sigmoid-shaped curve is produced. With the lag phase varying between 30 minutes and 3 hours in duration, another unknown is factored into any such assessment of time since death. The causation remains unknown but indicates either continued heat production as a result of anaerobic metabolism or the preven- tion of heat loss from tissues, possibly through the insulating effects of clothing or bed linen. Further research has even suggested the presence of double or triple exponential curves, depending upon the anatomical site of reading. In order to overcome this anomaly, algorithms and nomograms particular to each anatomical site examined have been developed.6–10 The most frequently referenced nomogram was described by Henssge et al.3 for use with rectal temperatures. The assumption that the individual’s core temperature is at a “normal” level at death also may not hold true. Stress, fevers, cold exposure, metabolic disorders (e.g., thyroid disease), peripheral vascular disease, and the individual’s age all could affect the temperature in the antemortem period. The cooling rate in a nonexperimental environment also is dependent upon on numerous factors, such as the variation in ambient temperature over the time frame The Timing of Death 191 that the body has lain exposed, the presence of wind passing over the body, precipi- tation, body posture (as a result of altered surface area exposed), the presence (or absence) of clothing, and the body mass index of the deceased.3 More recent advances have utilized infrared digital thermometers placed within the external auditory canal. The underlying concept is that, in life, the internal carotid artery perfuses the tympanic membrane; thus the temperature is identical to the core body temperature. The results indicate that single temperature measure- ments recorded from this site can provide accurate methods of estimating the time since death up to 16 hours postmortem when used in collaboration with a standard algorithm such as Henssge’s nomogram for the brain.11 Also of note, unlike other sites where double or triple exponential cooling curves resultant from lag phases are well documented, there appears to be no lag phase associated with estimations based on the external auditory canal, resulting in a single exponential curve.11,12 External auditory canal-based estimations are, however, affected by head position, the presence of wind passing over the cadaver, and natural circadian temperature alterations during the antemortem phase.11 Rigor Mortis Rigor mortis, or postmortem rigidity, commences after a 3- to 6-hour period of muscular flaccidity at death and lasts up to 36 hours, after which it diminishes.13 Ultrastructurally, skeletal muscle is composed of two main components: actin and myosin. The interaction between the two proteins produces contraction of individual sarcomeres, resulting in the contraction of muscles in their entirety. The release of the contraction, and hence the commencement of muscular relaxation, is a process that is dependent upon the concomitant binding of adenosine triphos- phate (ATP). The subsequent hydrolysis into adenosine diphosphate (ADP), via an ATPase, releases energy that frees the actin–myosin protein complex.3 The ATP is resynthesized to allow subsequent contractions, with energy for this chemical con- version originating from glycogen. After death, glycogen resources are rapidly depleted, thus preventing the energy-dependent “breaking” of sarcomere contractions and resulting in rigor mortis. Although previously disputed, true sarcomere shortening similar to antemortem muscle contraction has now been proven to cause rigor mortis.14–16 As autolysis commences and the ultrastructural cellular components lose their integrity, the rigor is “released”. In 1811 the first descriptive study was reported by Nysten, who considered that rigor occurs predictably first within the temporomandibular joint passing inferiorly to the limbs in a descending and ordered manner. Although it was assumed that rigor progresses simultaneously in all muscles, the causation of the apparent sequence was suggested to result from the difference in muscle volume at these sites.17,18 However, later work has disproved this theory, instead explaining the difference through the varying proportion of red and white fibers in individual muscles, the dynamic characteristics of each joint (e.g., the elbow is inherently more mobile than the jaw), and the differences in temperature of each muscle.14 By recognizing the status of rigor mortis within a cadaver, estimates for time since death can be provided. Unfortunately, many factors affect the onset of rigor, notably the temperature of the environment, the degree of muscular activity prior to death, and the age of the deceased.13 Therefore, despite numerous publications claiming to demonstrate accurate estimation of the PMI based solely upon the nonsubjective assessment of rigor mortis, little progress has occurred in the field. 192 Essentials of Autopsy Practice Livor Mortis Livor mortis, or hypostasis, describes the red-blue hue created in the absence of a cardiovascular circulation by the gravity-dependent accumulation of blood within small cutaneous or visceral vessels. The spectrum of coloration is great, depending not only on premortem conditions but also on the time since death.13 Attempts have

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