Comparison of GSR Composition Occurring at Different Locations Around the Firing Position

Abstract: Variations in gunshot residue (GSR) compositions are used in the reconstruction of shooting incidents. In this study, GSR samples taken from seven different locations around and in the firearm were collected and analyzed using scanning electron microscopy/energy dispersive X‐ray analysis. Four different types of ammunition were applied. Very low correlations were found when different ammunition were used. This clearly shows that it is possible to differentiate between ammunition types. When the same ammunition was used, high correlations were found between samples taken from external positions (such as hands of shooter, bullet‐entrance holes) but poor correlation was found between internal samples (such as firearm barrel, cartridge case) and external samples. A high degree of association was found between samples that simulated victim and shooter. These findings clearly demonstrate that GSR comparison studies are meaningful but care needs to be taken when choosing suitable exhibits. External samples (such as hands of shooter, bullet‐entrance holes) are more suitable candidates than internal samples (barrel of the firearm, cartridge case).     

The Relationship Between the Surface Morphology and Chemical Composition of Gunshot Residue Particles

In this study, chemical composition and morphology of gunshot residue (GSR) of 9 × 19 mm Parabellum‐type MKE (Turkey)‐brand ammunition were analyzed by scanning electron microscope and energy dispersive X‐ray spectrometer. GSR samples were collected by “swab” technique from the shooter's right hand immediately after shooting. According to general principles of thermodynamics, it is likely that the structures will have a more regular (homogeneous) spherical form to minimize their surface area due to very high temperatures and pressures that occur during explosion. Studied samples were collected under the same conditions with the same original ammunition, from the same firearm and a single shooter. This is because many other variables may affect size, structure, and composition in addition to the concentrations of elements of the structure. Results indicated that the chemical compositions are effective in the formation of GSR morphological structures.     

Characterisation of gunshot residue from three ammunition types using suppressed anion exchange chromatography

Gunshot residue (GSR) is commonly analysed in forensic casework using either scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) or gas chromatography-mass spectrometry (GC-MS). Relatively little work has been reported on the post-discharge GSR content of non-metallic inorganic or low molecular weight organic anions to distinguish between different ammunition types. The development of an analytical method using suppressed micro-bore anion exchange chromatography (IC) is presented for the analysis of GSR. A hydroxide gradient was optimised for the separation of 19 forensically relevant organic and inorganic anions in <23min and sensitivities of the order of 0.12-3.52ng of anion detected for all species were achieved. Along with an optimised extraction procedure, this method was applied to the analysis of post-ignition residues from three selected ammunition types. By profiling and comparing the anionic content in each ammunition residue, the possibility to distinguish between each type using their anionic profiles and absolute weight is presented. The potential for interference is also discussed with respect to sample types which are typically problematic in the analysis of GSR using SEM-EDX and GC-MS. To the best of our knowledge this represents the first study on the analysis of inorganic anions in GSR using suppressed ion chromatography.     

Distribution of GSR particles in the surroundings of shooting pistol

Several series of experiments were performed to study the distribution of GSR particles in seven directions in the surroundings of shooting firearm (pistol CZ 85 caliber 9 mm Luger). External and internal conditions and two different primer types were used for the shooting experiments. The results showed that maximum number of GSR particles could be found in the right front quadrant at a distance of 2–4 m with respect to the shooting firearm position and shooting direction. GSR particles were even found in distance 10 m from shooting firearm. A significant influence of climatic conditions on GSR distribution was confirmed.     

Time periods of GSR particles deposition after discharge-final results

The elemental objects of the research study are: determination of time periods corresponding to gunshot residue particles (GSR) deposition after the shot from selected pistols and a revolver, and evaluation of the deposited particles number. For several shooting experiments were used a pistol CZ model 85, caliber 9 mm Luger with common ammunition 9 mm Luger FMJ Sellier & Bellot, a pistol CZ model 70, caliber 7.65 mm Browning (32 ACP) with common 7.65 mm Browning FMJ Sellier & Bellot ammunition and a revolver S&W Modell 60, barell length 2-1/8', cal. .38 Special with common Sellier&Bellot (FMJ) ammunition. The results of the study have indicated the behavior of GSR particles deposited after a single discharge. The overall time interval of GSR particles deposition and the number of deposited particles with the above mentioned arms and ammunition were established. The results can potentially be used for clarifying the situation at crime scenes and for subsequent interpretation of GSR evidential value in caseworks.     

A comparative study of gunshot residue originating from 9 mm Luger ammunition from various producers

Following previous work on differentiation between gunshot residue according to the type of ammunition used, a specific investigation was undertaken of traces originating from 9 mm Luger ammunition using SEM-EDX. The aim of this study was to determine whether GSR originating from this type of ammunition is similar, or whether differentiation could be made between particular manufacturers of Luger ammunition. The results were collected in the form of counts of particles in each of seven key elemental classes being combinations of lead, antimony and barium. These were then adjusted to a factor known as frequency of occurrence which allows comparison of the distribution of particles within the classes between samples with differences in absolute particle counts. The relationships between the samples were examined using non-parametric statistical tests: R-Spearman and tau-Kendall rank correlation coefficients. It has been found that most of the studied samples of GSR were similar to each other despite their originating from various manufacturers.     

Fate and Behavior of Gunshot Residue: Recreational Shooter Vehicle Distribution

The susceptibility for recreational shooters to transfer gunshot residue (GSR) to both the interior and exterior of a vehicle is investigated. A comprehensive sampling protocol was used to assess the most likely areas of GSR transfer from recreational shooter contact, such as the steering wheel and the area, the firearms were stored (the trunk). Up to 315 characteristic GSR, particles were found in several locations throughout the interior of a vehicle. As many as 876 characteristic particles were found throughout a single vehicle. The data indicate that vehicles frequently occupied by firearms users are a potential source for inadvertent transfer of GSR to persons unrelated to firearm activity. In criminal cases where vehicles have been used, such transfer processes for GSR need to be considered within the context of any case interpretation. The implications for subsequent contamination and transfer processes from such vehicles require further investigation.     

Grouping of ammunition types by means of frequencies of occurrence of GSR

An attempt was made to build a classification scheme for gunshot residues (GSR) samples originating from four types of ammunition, collected from shooters' hands immediately after shooting. The secured material was examined with the use of SEM-EDX method in the automatic manner. The obtained results were expressed as frequencies of occurrence of particles assigned to various chemical classes. In order to establish the most discriminative of these features the Mann-Whitney test was performed. Cluster analysis was performed for grouping the analysed samples according to their origin, i.e. the type of ammunition. It has been found that samples of GSR originating from Browning 7.65 mm and Luger 9 mm ammunition can be fairly easy differentiated from the remaining samples, whereas samples of GSR originating from of Makarov 9 mm and these of Tokarev 7.62 mm could not be differentiated using frequencies of occurrence of particles in the selected chemical classes.     

A study of dispersion of gunshot residue from a frequently used Serbian ammunition cal. 7.65 mm to support selected aspects of casework in North Macedonia

The subject of this research was the inorganic gunshot residue component collected from shooting patterns obtained on woven cotton cloth using a Pietro Beretta model 70 pistol, cal. 7.65 mm and Serbian ammunition for the following muzzle-to-target distances: 25, 50, 75, 100 and 125 cm. For each distance, three rounds of shooting were performed. Particles were lifted within a 10 cm radius of the projectile entrance and automatically analyzed using a scanning electron microscope coupled with an energy dispersion X-ray spectrometry. The obtained data on the populations of particles were analyzed taking into account their numbers, chemical classes and sizes. The results showed an apparent maximum incidence within all particles containing barium at about 50 cm distance. Also, lead particles revealed a distinct behaviour, being dominant at a 25 cm distance, falling below the other chemical classes, and finally becoming dominant again at 125 cm. The analysis of the frequency of occurrence of particles sorted according to their sizes confirmed that the small particle population is the largest, and their distribution in function of the equivalent circle diameter is exponential-like. The obtained results provided knowledge on the distribution of particles in the vicinity of the tested firearm and ammunition cal. 7.65 mm which generally corroborates with similarly studied GSR distributions obtained for the use of pistols cal. 9 mm. This information, together with the examinations of gunshot damages and other types of residues such as soot or unburned propellant grains may support qualitative inferences on shooting distance estimation, especially in cases, when the firearm and cartridges are not available to perform test shooting. In such cases even roughly estimated shooting distance can be helpful, e.g. for confirming or excluding the possibility of self-inflicted injuries or suicide and infer on the mutual position of the shooting stage actors. An example of casework that illustrates intermediate shooting distance estimation is presented.     

Towards the protection of ammunition headstamps during fingermark enhancement processing; a preliminary study

Forensic recovery from fired ammunition casings remains one of the most challenging tasks during high-profile investigations. Often, the decision must be made between screening for DNA or fingerprints, and, in doing so, the impact these processes will have on the examination of ballistic markings imparted on the ammunition from the firearm itself. Traditionally, fingermark enhancement processes have yielded low success rates in their efforts to identify suspects by enhancing friction ridge detail left on the cartridge casings. Moreover, the enhancement methods utilised may often induce detrimental physical changes to the casing(s), rendering them unsuitable for subsequent ballistics (marking) examination. Recently, new technology has been shown to increase the success rate of fingermark recovery from fired ammunition, and the growing adoption of such innovation means that new challenges are encountered to maximise evidence recovery and streamline forensic workflows. One such example arises from the potential obscuration of the ammunition headstamp area during such treatments. Accordingly, this study outlines the preliminary investigations and developments of a polymer mask substrate that serves to protect the headstamp of fired ammunition casings during relevant fingermark enhancement processes. The technique also has the capacity to be used as a surface protection device to eliminate unwanted chemical deposition across other areas of interest and evidence types.     

Glass-containing gunshot residue particles: a new type of highly characteristic particle?

In 0.22 caliber rimfire ammunition, the primer often contains lead or lead and barium compounds. As residues from these primers do not contain lead, barium, and antimony, they cannot be uniquely classified as gunshot residue (GSR) under ASTM designation E 1588-95. In many types of 0.22 caliber rimfire ammunition, the cartridge contains a primer sensitized with glass. In this paper we describe a previously unreported type of GSR particle consisting of glass fused with other primer components. As there appear to be few potential environmental or occupational sources of particles composed of lead and barium compounds fused to glass, particularly borosilicate glass, these particles may have high evidential value. Scanning electron microscopy with energy dispersive X-ray detection (SEM-EDX) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were evaluated for the characterization of glass-containing GSR particles. The occurrence of glass-containing GSR particles was established in the residue from various brands of 0.22 caliber ammunition, and several sub-types were identified.     

Gunshot residue testing in suicides: Part I: Analysis by scanning electron microscopy with energy-dispersive X-ray

Several different methods can be employed to test for gunshot residue (GSR) on a deceased person's hands, including scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM-EDX) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Each of these techniques has been extensively studied, especially on living individuals. The current studies (Part I and Part II) were designed to compare the use and utility of the different GSR testing techniques in a medical examiner setting. In Part I, the hands of deceased persons who died from undisputed suicidal handgun wounds were tested for GSR by SEM-EDX over a 4-year period. A total of 116 cases were studied and analyzed for caliber of weapon, proximity of wound, and results of GSR testing, including spatial deposition upon the hands. It was found that in only 50% of cases with a known self-inflicted gunshot wound was SEM-EDX positive for at least 1 specific particle for GSR. In 18% of the cases there was a discernible pattern (spatial distribution) of the particles on the hand such that the manner in which the weapon was held could be determined. Since only 50% of cases where the person is known to have fired a weapon immediately prior to death were positive for GSR by SEM-EDX, this test should not be relied upon to determine whether a deceased individual has discharged a firearm. Furthermore, in only 18% of cases was a discernible pattern present indicating how the firearm was held. The low sensitivity, along with the low percentage of cases with a discernible pattern, limits the usefulness of GSR test results by SEM-EDX in differentiating self-inflicted from non-self-inflicted wounds.     

Physical forms of contemporary small-arms propellants and their forensic value

Intermediate gunshot wounds typically produce powder tattooing and/or stippling of the skin. The size and density of such powder-induced injuries around an entry wound are used to estimate the separation distance between the muzzle of the responsible firearm and the entry site through test firings at selected muzzle-to-target distances, with ammunition comparable to the injury-producing round and the evidence firearm. The foregoing is well known to forensic pathologists who document and describe such powder patterns in gunshot victims and firearm examiners who customarily produce the test-fired powder patterns for subsequent range-of-fire determinations. Less known, particularly to pathologists, is the considerable variety in forms of modern nitrocellulose propellants, their effects on powder-induced injuries to human skin, and the value of these varied physical forms in the reconstruction of shooting incidents. These factors are the subject of this article.     

An investigation on the secondary transfer of organic gunshot residues

Gunshot residues (GSR) are an important forensic trace in firearm-related events. Currently, routine GSR analyses focus on the detection and characterisation of the inorganic components (IGSR). The increasing prevalence of heavy metal-free ammunition challenges these current protocols and there is an increasing interest in how the organic components of GSR (OGSR) can provide complementary information. Similar to the situation with IGSR, OGSR compounds originally deposited on the shooter during the firing process may further be transferred onto another individual or surface. Hence, the aim of this study was to provide additional information regarding the risk of a secondary transfer of OGSR. Two scenarios were investigated, the first one related to the arrest process and the possibilities of a secondary transfer arising between a shooter onto a non-shooter (e.g. between a police officer and a person of interest (POI)). The second scenario concerned the transfer of OGSR onto the non-shooter after handling a firearm for few minutes without discharging it. One calibre was chosen, the .40 S&W calibre, used by several Australian State police forces. A secondary transfer was observed in all cases for the two scenarios investigated, for three compounds of interest: ethylcentralite (EC), diphenylamine (DPA), N-nitrosodiphenylamine (N-nDPA). The firearm handling scenario resulted in a larger secondary transfer to that of the arrest scenario. Overall, the amounts of OGSR detected on the non-shooter were generally lower than that detected on the shooter and controls after the arrest scenario. The results of this study provide complementary knowledge about OGSR, which can be further used to improve the current practice and the interpretation of OGSR evidence. In particular, it highlights that the secondary transfer proposition must be considered during the interpretation of forensic findings, especially when small amounts of OGSR target compounds are detected.     

Distribution of lead and barium in gunshot residue particles derived from 0.22 caliber rimfire ammunition.

0.22 caliber rimfire ammunition is commonly encountered in firearms incidents in Australia. This paper reports on work which has confirmed the nonhomogeneous nature of gunshot residue (GSR) particles and that the lead and barium distribution within particles varies significantly with the particle size and structure. The outcome has been an improved understanding of how the particle formation influences the ability to determine the origin of GSR derived specifically from 0.22 caliber rim fire ammunition.     

Gunshot residue particles formed by using ammunitions that have mercury fulminate based primers.

Ammunition having mercury fulminate-based primers are commonly manufactured by Eastern Bloc countries and used extensively in the Middle East. Gunshot residue (GSR) particles formed by firing these types of ammunition were examined. It was observed that much lower percentage of mercury-containing GSR particles were found in samples taken from a shooter as compared to the percentage of such particles in samples from cartridge cases. This fact must therefore be taken into account when interpreting case results. A plausible explanation for the results described is proposed.     

Environmental assessment of gunshot residue particles in the public domain of the United Kingdom

Only limited data currently exists on the inadvertent transfer of gunshot residue (GSR), or GSR-like particles through contact with public places. In this study, an assessment occurrence of GSR in public environments in England, UK was undertaken. Utilizing a stubbing sampling technique over 260 samples were collected from areas accessible to the public, including buses, trains, taxis, and train stations. Stub analysis was performed by Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM-EDX). The results showed no characteristic GSR particles were detected on any of the 262 samples taken. From these samples, a total of four indicative/consistent particles were identified on one train seat (2× BaAl, 2× PbSb). Although geographical location and firearm association is likely to influence GSR occurrence, the data suggests that the potential for inadvertent GSR transfer through contact with public transport and associated communal areas is insignificant. Further research assessing environmental background levels of GSR in additional geographical locations is critical in an evaluation of the potential for GSR transfer from the environment.     

SEM/EDS analysis and characterization of gunshot residues from Brazilian lead-free ammunition

The exposition to heavy metal-rich airborne due to fire practicing has forced to the development of heavy metal-free environmental ammunition primers all over the world. Here we characterize the GSR elements present in the Brazilian lead-free ammunition produced by Companhia Brasileira de Cartuchos (CBC) and commercialized by MagTech in the U.S. and Europe under the name CleanRange centerfire cartridges. Both first and second generations of CleanRange in calibers 9 mm Luger, .40 S&W, .380 AUTO and .38 SPL were analyzed and compared to regular Brazilian CBC ammunition by scanning electron microscopy/energy dispersive spectroscopy. Differences in composition and morphology of GSR particles from the two generations of CleanRange were observed. The first generation ammunition (found in Europe) presented spherical particles, being strontium the only unique element detected. The second generation (found in the U.S.) produced irregular particles composed mostly by potassium, aluminum, silicon and calcium. We can conclude that identification of GSR derived from CBC second generation lead-free ammunition in suspects' hands may be impossible without the addition of a distinct metallic taggant in the primer composition by the manufacturer.     

Discharge of a Pistol Out a Car Window with the Breech Within the Interior of the Car: Analysis of Gunshot Residue on a Car's Interior Surfaces

The defendant, the driver of the questioned car, allegedly extended his right arm over the passenger seat and fired a single shot from a 380 pistol out the passenger window with the pistol's breech within the car. A simulation of this shooting scenario using the same model car, but different year, was conducted to quantitate gunshot residue (GSR) contamination of interior surfaces within the car. The test car's dash and headliner/window frame above the pistol had the heaviest GSR contamination. The dash GSR from airborne deposition documents a firearm discharge within the vehicle. Transfer from GSR‐contaminated hands or clothing to the dash is unlikely. The heavy GSR contamination of the headliner/window frame above the pistol likely documents the window from which the pistol was fired, but additional experiments are needed to verify.