J Forensic Sci, May 2014, Vol. 59, No. 3 doi: 10.1111/1556-4029.12409 TECHNICAL NOTE Available online at: onlinelibrary.wiley.com CRIMINALISTICS Kyla L. Kersh,1 M.S.; James M. Childers,1 Ph.D.; Dale Justice,2 B.S.; and Greg Karim,2 A.S. Detection of Gunshot Residue on Dark- Colored Clothing Prior to Chemical Analysis ABSTRACT: Detection of gunshot residue (GSR) is an arduous task for investigators. It is often accomplished with chemical tests, which can reveal elements and ions indicating the presence of GSR, but are likely to cause physical alteration to the pattern. In this study, the Spex Forensics Mini-CrimeScope MCS 400, along with 16 accompanying wavelength filters, was applied to various GSR patterns and target types. Three dark shirt materials, four ammunition calibers, and eight ammunition manufacturers, along with the primer residue of the different manu- facturer ammunitions were tested. Results indicate the alternate light source wavelength of 445 nm to be the optimal setting. In addition, target material plays a large role in the preservation of GSR patterns as particles burn. Furthermore, it can be extrapolated that residue, observed from a full round and firing distance of six inches, is mostly composed of unburnt gunpowder residue, not primer residue. KEYWORDS: forensic science, gunshot residue, gunpowder residue, primer residue, firearm, alternative light source In 2010, there were 14,748 known murder cases in the United photographic paper to examine the size of the GSR pattern due States. Of the cases to which additional data were available, 8,775 to the imprint of nitrites. Once the MGT has been completed, murders involved firearms; approximately 60% of all murder cases. the sodium rhodizonate test is commonly performed to test for In addition, there were 367,832 robberies and 778,901 aggravated lead. Other tests that can be used include the Harrison and Gill- assaults; of these, 127,521 and 137,857 cases involved firearms, roy test, which tests for lead, barium, and antimony, or the respectively (1). Due to the common use of firearms in violent Lunge test, which tests for nitrocellulose (3). Although many of crimes, it becomes important to analyze such evidence in the search these tests have traditionally been used for years, there are a for information relevant to the reconstruction of the event. Gunshot number of disadvantages. Any GSR examination that is needed residue (GSR) is an important type of firearm-related evidence but (e.g., sample to be placed in a scanning electron microscope for remains one of the most difficult subjects to study due to the many elemental composition) must be performed prior to chemical variables (e.g., target type, environmental conditions, firearm and testing, because the chemical testing could be destructive; any bullet caliber, gunpowder and primer composition, etc.). pattern or physical sample that was present will most likely be When searching for GSR at a crime scene, it can sometimes destroyed. For example, a hypothesis of Bailey, Casanova, and be problematic. A bullet entrance on the victim might be easy to Bufkin (4) was to use sodium hypochlorite or bleach to make locate, but the surrounding GSR cannot be seen due to the dark patterns easier to see on dark- or multicolored fabrics. The MGT clothing on which it is located. The same challenges can be and sodium rhodizonate tests were then performed. This exten- applied to the alleged shooter; dark-colored clothing easily sive application of chemicals may have initially provided neces- masks traces of GSR. With the use of chemicals, it is possible to sary information for the researchers, but finally reduced the confirm the presence of suspected GSR on certain substrates. integrity of the evidentiary sample once all was completed; the The modified Griess test (MGT) is one of the most commonly sample cannot be returned to its original state for additional used techniques to test for nitrites generally known to GSR. To analysis. begin the MGT, a piece of desensitized photographic paper is This study focuses primarily on the ability to quickly and effi- treated with sulfanilic acid in distilled water, along with ciently detect possible traces of GSR on dark-colored clothing in a-naphthol in methanol. The treated photographic paper is a nondestructive manner through the use of an alternative light placed on the front of the sample to be tested, and the back of source (ALS). For this purpose, it is hypothesized that results the sample is steam ironed with dilute acetic acid solution. If will identify an ideal wavelength of light while taking into con- nitrites are present, a reaction between the chemicals on the front sideration certain variables (i.e., fabric type, caliber/firearm type, and back of the sample causes orange-colored specks to appear and manufacturer differences of the same caliber). When using on the photographic paper (2). The examiner can then use the an ALS, it is postulated that different fabric blends will have varying results on the visualization of GSR. Primer residue will also be tested separately to identify any visual differences 1 Texas Tech University, Institute for Forensic Science, 4434 South Loop between gunpowder residue and primer residue in hopes of 289, Lubbock, TX. 2 determining which may be fluorescing. Theoretically, once the Austin Police Department, Forensic Science Division, Firearms & Tool- marks, 812 Springdale Road, Austin, TX. assumed GSR patterns are located, multiple measurements and Received 14 Aug. 2012; and in revised form 15 Mar. 2013; accepted 24 pictures can be taken in an effort to form preliminary inferences. Mar. 2013. It would then be feasible to take physical samples for analysis 754 © 2014 American Academy of Forensic Sciences KERSH ET AL. DETECTION OF GSR 755 within the laboratory and perform chemical tests of a sample fur- lar to Oomen and Pierce (9). This technique was able to produce ther confirming its identity as GSR. elemental mapping of GSR from various sources (e.g., skin and fabric); however, m-XRF is limited to flat sample sizes of 20 9 20 cm and can take 3–4 h to process. An Overview of Gunshot Residue Gunshot residue analysis provides information that can be crit- Alternative Light Sources ical to the outcome of a criminal investigation: (a) determination of entry and exit wounds, (b) estimation of shooting distance, Sunlight, which makes up the electromagnetic spectrum, is (c) establishment of the type of ammunition used, (d) the trace composed of (a) visible light, 400 nm to 700 nm; (b) infrared of the projectile trajectory, (e) relation of an individual to the light, greater than 700 nm; and (c) ultraviolet light, less than shooting incident, and (f) incorporation of all the above elements 400 nm. Ultraviolet (UV) light can be further broken down into into the reconstruction of the crime scene (5). Primer residue three categories: (a) UV-A (or black light), 320 nm to 400 nm; and other GSR escape the gun in the form of gases. Once the (b) UV-B, 290 nm to 320 nm; and (c) UV-C, less than 290 nm. gases condense, due to the high temperature and pressure created To utilize any of these wavelengths for the purpose of examin- from firing, it will form spheroidal-shaped sediment on the fire- ing evidence, certain filters must be applied, such as long-pass, arm and surrounding objects, usually 0.5 to 5.0 lm in diameter short-pass, or band-pass filters. Long-pass filters allow longer (6). Previous studies have shown that people standing three feet wavelengths through the filter while blocking shorter wave- or closer to the side of the shooter will probably have GSR on lengths. Short-pass filter alternatively allows shorter wavelengths their hands, whereas people standing 10 feet or further in the to pass through while blocking longer ones. A band-pass filter same direction will likely not have GSR on their hands (7). allows only a narrow band of wavelengths through. The interac- There are a number of factors that could affect the availability of tion of light with matter can be important for enhancing the visi- GSR on the victim or shooter: distance, caliber, types of propel- bility of evidence at a crime scene. The absorption of light lant, type of weapon, target material, and muzzle-to-target angle occurs when a given wavelength is absorbed by a molecule’s (4). electrons and causes the molecule to appear darker than the sur- The majority of GSR consists of burnt and unburnt particles rounding environment. This is commonly seen when detecting from the propulsive charge and primer used by the individual or bloodstains on fabric substrates. Reflection of light occurs manufacturer. Typically GSR is a composite of lead styphnate because the free electrons within the matter do not permanently (initiator), barium nitrate (oxidizer), and antimony sulfide (fuel) absorb the light and instead release it almost immediately. Scat- (8). The propellant mixture and the primer particles encompass tered light is a form of reflection: light is reflected in random most of the organic compounds, including nitrocellulose (NC) directions due the roughness of the surface to which it is applied and nitroglycerine (NG). Smokeless gunpowder is single, double, (e.g., dust particles, hair, and fibers scatter light in various direc- or even triple based. Single-based powders contain NC as the tions). As electrons of an object do not interact with incoming explosive component, while double-based contain both NC and light, but merely pass through, transmission takes place. Sub- NG. A portion of the NC/NG mixture is replaced with nitrogua- strates such as glass and clear plastic allow transmission of light. nidine in a triple-based powder.