Review ArticleOpen Access

Comparison of Gunshot Residue Visualization with Alternative Light Sources and Infrared Light

Mark Vecellio*

Methodist University Applied Forensic Science Program

*Corresponding Author: 
Mark Vecellio
  Methodist University Applied Forensic Science Program
  5400 Ramsey Street, Fayetteville
  North Carolina 28301.
  Tel: 910-630-7000
  E-mail: [email protected]

Citation: Mark Vecellio (2020) Comparison of Gunshot Residue Visualization with Alternative Light Sources and Infrared Light. J Forensic crime investi 3(1): 104

Abstract

This study examines and contrasts known methods of investigating and visualizing components of gunshot residue (GSR) on dark colored surfaces: UV-VIS alternative light source (ALS) and infrared (IR) light. The authors fired four types of ammunition (.22, .223, 9mm, .45) five times each from a distance of six inches into two substrates: 1) black, cotton tee-shirt; 2) drywall painted with Valspar Black Gloss paint. The samples were later observed using UV-VIS wavelengths (395 nm, 450 nm, and 530 nm) and a Fuji XT1 IR camera with IR 695 and 830 camera filters. GSR was visualized on all 20 cotton tee shirt fabric samples using IR (both filters) and ALS 450 nm. Regarding the ALS, 530 nm allowed visualization of GSR on 14 of the 20 samples, while 395 nm allowed visualization of GSR only on seven of the 20 samples. GSR was not identified on any of the painted drywall samples using any of the light sources. The findings support previous research that both ALS and IR sources may be helpful in locating GSR when unaided visualization is not possible. In this study, ALS was more effective in visualizing scattered GSR while IR was more effective in visualizing bullet wipe, scorching, and burning.

Keywords: Gunshot Residue; Infrared Light; Infrared Imaging; Alternative Light Source; Alternate Light Source; Gunpowder Residue; Firearm;

Background

GSR is composed of smoke resulting from combustion of propellant, metallic fragments from the bullet, unburned and partially burned gunpowder particles, primer residues, and lubricants [1-3]. GSR may be deposited on surfaces of objects at a crime scene or on clothing or skin of persons present during a weapon discharge. Though not all components of GSR can be visualized by the unaided eye, this study is focused on the components that are generally visible when GSR is deposited on light colored surfaces. These components may consist of gunpowder discharge residue and bullet wipe and are typically analyzed by forensic scientists to determine muzzle to target distance [1-3], analyze gunshot wounds [4,5], distinguish entry from exit defects in fabric [4,6], and assist in the overall analysis and reconstruction of the crime scene [2,4].

Effective visualization of GSR is an important task during crime scene processing and evidence searches, especially given its fragile nature which requires prompt collection and preservation to avoid destruction or contamination [1,2].

Some components of GSR are easily observed on light colored surfaces due to color contrast between the residue and the surface on which it was deposited. Dark surfaces, however, often mask the GSR. Chemical methods are sometimes used to detect nitrites and thus presumptively identify GSR; however, these methods are potentially destructive [7,8].

The two methods chosen for this research include infrared light (IR) coupled with an IR camera and alternative light sources (ALS). These methods can provide a quick, efficient means of obtaining data useful during preliminary stages of an investigation but are not intended to replace scientific testing performed by qualified firearms examiners. The primary aim of this study is to qualitatively analyze and compare the two visualization methods involving the use of UV, visible wavelengths, and IR. This research may have value to practitioners whose duties include crime scene and evidence processing, and more specifically, locating and collecting GSR evidence.

IR has been shown in previous research to help visualize latent evidence by creating contrast in color between the evidence and the background substrate [9-13]. Evidence successfully visualized with IR in previous studies includes obscured ink [10,11] blood [12], and GSR deposited from 9mm and 44 caliber ammunition [9, 13-15]. Bailey [13] visualized and photographed GSR patterns on ten different dark and multicolored fabrics using sunlight as the source of IR. The source of IR used in Lin’s study [9] is unclear. Barrera et al. [14] used a Dedolight light as the IR source and was able to visualize GSR on 18 of 26 dark colored fabrics. Rhodes et al. [15] used an Attestor Forensics Scene View BU800 as the source of IR and was able to visualize GSR on four different dark colored fabrics. One of the objectives of this study is to use relatively inexpensive portable incandescent light sources to provide the IR since natural sunlight is not always a feasible option for investigators and agency budget limitations may impede access to expensive equipment.

ALS systems, using a variety of wavelengths of light in conjunction with filters, have been used to identify various forms of latent evidence by producing fluorescence, which allows contrast in color to be developed between the evidence and background substrates [16-19]. Barrera, et al. [14] used a Lumatec Superlite 410 ALS and a variety of wavelengths to study GSR patterns on 26 fabrics. Barrera, et al. [14] found that 440 nm was the preferred wavelength to visualize GSR from .44 caliber ammunition, though results were not provided for other wavelengths used in the study. Kersh, et al. [19] used a Spex Forensics Mini-CrimeScope 400 with 16 accompanying filters to create fluorescence and help visualize GSR from 9mm, .357, .40, and .38 caliber ammunition. Kersh, et al. found that a 445 nm wavelength was most effective for visualizing GSR across a variety of substrates. An objective of this study is to determine if different ALS brands and models, with different wavelengths, would provide results consistent with previous studies. In addition, because the type of firearm and ammunition are critical factors in GSR deposition [1,2,4], different firearms and ammunition were used in this study.

Materials

Substrate materials used in this study included black colored, 100% cotton tee-shirts and ToughRock drywall painted with Valspar Black Gloss Latex Enamel paint. All of these materials are commonly available at retail stores in the United States. The cotton tee shirts were cut and stapled to targets. The drywall was painted, air-dried, and cut into segments. The drywall was then affixed to targets.

A Springfield Model 45 XD handgun was used to fire S & B .45 Auto 23 grain full metal jacket (FMJ) ammunition. A Sig Sauer .22 long rifle caliber handgun was used to fire CCI Minimag .22 long rifle caliber, 36 grain pleated lead hollow point ammunition. A DPMS Model AR 15 was used to fire Winchester .223 Remington caliber, 55 grain FMJ ammunition. A Ruger Model LC9 was used to fire Winchester 9mm Luger caliber, 115 grain FMJ ammunition.

The ALS units utilizing UV-VIS wavelengths used in this study consisted of the Sirchie TMX (395 nm and 450 nm) and the Sirchie Megamax (530 nm). To enhance visualization of the GSR, orange goggles were used in conjunction with the 450 nm wavelength and red goggles were used in conjunction with the 530 nm wavelength. These wavelength and filter combinations are widely recognized as effective methods of visualizing various forms of latent evidence [15-17]. The emitted wavelength creates fluorescence while the goggles serve to filter the original wavelength, thus enabling the fluorescence to be visualized. Nikon D5200 DSLR cameras and close-up Nikkor 40mm lenses were used to capture images of the samples illuminated by ALS UV-Vis wavelengths . A Tiffen Orange 21 filter was used in conjunction with 450 nm. A Tiffen Red R2 filter was used in conjunction with 530 nm.

A Fuji XT1 IR camera with Neewer IR 695 and IR 830 filters, in conjunction with portable 100-watt incandescent light sources, was used to observe and photograph the samples illuminated by IR. The IR 695 filter blocks wavelengths below 695 nm while the 830 filter blocks wavelengths below 830 nm.

Method

The 200 participants in this experiment were graduate students at Tel Aviv University, Tel Aviv, Israel, who were engaged in research a variety of physical sciences, who agreed to participate in a short and interesting experiment to take place in their lab. Their average age was 31, with 115 female and 85 male. They were older than many graduate students in other countries because that had spent two or three years completing their compulsory military service.

Results/Discussion
Fabric Samples

IR and 450 nm blue light were equally effective in presumptively visualizing the presence of GSR on the dark colored fabric samples (Table 1). Both of these visualization methods resulted in visualization of GSR on 100% of the samples. The 530 nm green light resulted in the visualization of 14 of the 20 (70%) of the black shirt fabric samples. Notably, the 530 nm wavelength resulted in visualization of GSR on all of the 9mm and .22 ammunition samples. Ultraviolet 395 nm resulted in visualization of GSR on all of the 9mm ammunition samples, but was largely ineffective (20% positive visualization) for visualizing GSR on the remaining samples.

Light Source .22 9 mm .223 .45 Total
395 nm UV 0/5 5/5 1/5 1/5 7/20
450 nm Blue 5/5 5/5 5/5 5/5 20/20
530 nm Green 5/5 5/5 3/5 1/5 14/20
IR 5/5 5/5 5/5 5/5 20/20

Results Table (positive results/total samples)

The effectiveness of blue light in visualizing GSR on dark colored fabric is consistent with the findings reported by Barrera et al. [14] and Kersh et al. [19], who used different ALS systems. This study, when combined with the findings of Barrera et al. [14] and Kersh et al. [19], illustrates that blue light (450 nm in this study, 440 nm in the Barrera et al. study, and 445 nm in the Kersh et al. study) allowed effective visualization of GSR across a range of eight different weapons and types of ammunition. All three studies revealed that other ALS wavelengths are less effective than blue light.

In this study, though blue light (450 nm) and IR light were equally effective in identifying GSR on black colored fabric, the qualitative differences should be of interest to investigators. The GSR present on the cotton fabric samples was obscured under normal lighting conditions (Figures 1-2). The GSR observed with IR on cotton fabric effectively revealed scorching, blackening, and bullet wipe in proximity to the bullet hole (Figures 3-6), allowing clear evidence of the bullet entry site [1,4,5], while the GSR observed with ALS UV-VIS was scattered, and found up to five inches (12.7 cm) away from the bullet defects (Figures 7-10). The GSR identified with IR could be easily interpreted due to its close proximity to the bullet holes. The scattered GSR detected with ALS UV-VIS, however, could potentially cause interpretation difficulties when other trace particles are present. IR and 450 nm blue light, used in conjunction, may provide the most benefit by allowing visualization of bullet wipe, burning, scorching, and scattered particles.

Painted Drywall Samples

All visualization techniques were ineffective in visualizing GSR on the painted drywall samples. Though this study was limited to a single type of paint, the significance of this finding should be emphasized. Investigators should be aware that the inability to visualize GSR on painted surfaces cannot be interpreted as an absence of GSR. Additional study should be undertaken to develop suitable visualization techniques and to determine if other dark colored paints also obscure the presence of GSR.

Conclusions

The most effective ALS wavelength in this study was blue light (450 nm), which, when used with orange goggles and filters, identified 100 percent of GSR patterns on black, cotton fabric. This result is consistent with previous research [16]. UV 395 nm and green 530 nm resulted in varying degrees of success in visualizing GSR on black, cotton fabric. IR light used in conjunction with a Fuji XT1 IR camera and 695 and 830 filters effectively visualized 100 percent of GSR patterns on the black, cotton fabric samples used in this study. The ALS UV-VIS, particularly 450 nm, allowed effective visualization of scattered GSR particles while IR allowed effective visualization of burning, scorching, and bullet wipe. Employing both techniques, therefore, may maximize an investigator’s ability to visualize GSR and obtain meaningful, relevant information. This study expands upon existing literature which has revealed that ALS utilizing visible wavelengths and IR wavelengths may be useful in visualizing obscured GSR on a variety of dark and multicolored fabrics. ALS and IR, however, were both ineffective in visualizing GSR on drywall painted with Valspar Black Gloss Latex Enamel Paint.

Additional study could be undertaken to determine if the presence of blood impacts the effectiveness of the methods used in this study, to use ALS and IR to visualize GSR on other fabrics with different colors and pigments, to compare the results of this study with ammunition fired at different ranges, to examine whether other dark colored paints obscure the presence of GSR, and to develop methods of visualizing GSR on drywall painted with Valspar Black Gloss Latex Enamel paint.

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