Gunshot Residue Analysis Research Articles

The development of screen-printed electrodes modified with gold and copper nanostructures for analysis of gunshot residue and low explosives

Due to their portability, sensitivity, and ease of use, electrochemical sensors have recently become a popular method for rapid, on-site analysis. This study presents a proof of principle for the application of modified screen-printed carbon electrodes (SPCEs) for the detection of signature metals (Pb, Sb, and Zn) commonly found in gunshot residue (GSR), as well as for the detection of nitrate/nitrite in organic GSR and low explosives. To achieve these two aims, we have examined various electrode surface modifications. For metal detection, SPCEs were modified by electrodeposition of gold to improve sensitivity. GSR samples taken from two types of cartridge cases and shooting-related surfaces were analyzed using the Au-modified SPCEs. For nitrate/nitrite analysis, further electrode surface modifications were carried out by depositing Cu(II) onto the Au-SPCEs to enhance signal through catalytic activity of the copper surfaces. Both unburned and burned forms of black powder samples, as well as burned smokeless powder, were then analyzed using the Cu/Au-SPCEs. In conclusion, due to their low cost and portability, these sensors should prove useful for rapid forensic examination.

Police vehicle contamination by inorganic gunshot residue (iGSR) in Zagreb County Police Administration (Croatia): Analysis of characteristic and indicative particles across different vehicle parts and contributory risk factors.

Inorganic gunshot residue (iGSR) analysis, crucial for linking suspects to firearm use, faces challenges from potential environmental contamination, notably in police vehicles. The present study aimed to explore the level of iGSR contamination in police vehicles from the Zagreb County Police Administration (Croatia), considering particle types and their position in vehicles, and to identify associated risk factors. From December 2021 to April 2022, 65 of 86 police vehicles (margin of error: ±6% at a 95% confidence level) were sampled with GSR stubs on the drivers' seats, back seats, and backrests and analyzed using scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDX). Characteristic particles were found in 63.1% of vehicles, 33.8% on the driver's seat, and 24.6% on the back seat/backrest. Indicative particles were found in 70.77% of vehicles, with a fairly even distribution. McNemar's chi-square analysis showed no significant disparities in positive sample ratios across vehicle parts or particle types (p > 0.05). In total, 228 characteristic and 166 indicative GSR particles were identified, with no notable correlation among them (p = 0.346). Logistic regression analysis identified the transportation of individuals involved in firearms incidents as a statistically significant factor influencing the presence of characteristic particles (p = 0.030). The findings suggest a considerable prevalence of iGSR in the analyzed Police Administration unit, highlighting the need for careful contamination management in police operations to preserve evidence integrity, particularly in cases when individuals who used firearms had been transported in the vehicle.

Comparison of SEM-EDX and ICP-MS for the analysis of gunshot residues after burial: An experimental study

Gunshot residues (GSR) analysis can be valuable in a forensic context for distinguishing entry wounds from exit wounds, especially in cases when body alterations prevent macroscopic analysis. Several studies have demonstrated its usefulness in various contexts. However, few studies have examined the retention of GSR under environmental conditions particularly after burial.The primary objective of our experimental study is to investigate the retention of GSR after burial and decomposition by using two techniques: SEM-EDX and ICP-MS. Our secondary objective is to determine whether it is still possible to distinguish the entry wounds from the exit ones after 2 months of burial. For this study, we used a bovine model (cow feet), and fired with 7 mm semi-jacketed bullets. We formed several groups, including 3 control groups that hadn't been shot (buried for 2 days and 60 days and one unburied group), 3 test groups that had been shot (one unburied and two buried that were exhumed after 2 days and 60 days of burial).The results of our study show that both SEM-EDX and ICP-MS were suitable for detecting particles characteristic of GSR, after 60 days of burial. However, only SEM-EDX could differentiate easily the entry wounds from the exit ones.Our experimental study demonstrates that SEM-EDX analysis is suitable in cases where the discovery of a buried body doesn't allow the macroscopic determination of the ballistic trajectory.

Beyond the shot: Exploring secondary transfer of gunshot residue on common surfaces and the impact of hand cleaning methods

Understanding the presence, transfer dynamics and depletion of gunshot residues (GSR) on various surfaces is crucial for preserving evidence, reconstructing shooting incidents, and linking suspects to crime scenes. This study aims to explore the transfer and loss of GSR on commonly encountered surfaces such as ceramic, glass, metal, paper, and plastic, as well as the influence of different common hand cleaning methods on secondary transfer. Using scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) and automated detection software, we quantified highly indicative three-component characteristic particles (lead, barium, and antimony) on cups made from ceramic, glass, metal, paper, and plastic. Furthermore, we evaluated the amount of secondary transferred particles on these surfaces following various post-discharge hand cleaning methods: washing with water and soap, washing with only water, wiping with wet wipes, or using paper towels.The results demonstrate that counts of secondarily transferred GSR particles vary significantly among surfaces. Specifically, the transferred GSR count was highest on paper, followed by plastic, ceramic, metal, and glass respectively. Post-discharge hand cleaning methods, including washing with water and soap, washing with only water, cleaning with wet wipes, or with paper towel, resulted in substantial loss of GSR count on transferred surfaces. Among these methods, washing with water and soap showed the highest depletion. The empirical evidence provided by our results underscores the importance of considering surface properties, post-shooting activities, and the methods of sample collection and analysis when interpreting transferred GSR analysis. Despite challenges, these insights enhance our ability to link suspects to shooting crimes through careful consideration of the entire context.

IMPACTS of SUPERSONIC and SUBSONIC AMMUNITION on GUNSHOT RESIDUE DISTRIBUTION

In incidents where firearms are involved, the determination of the firing distance is one of the basic steps of the analysis aimed at determining the origin of the incident with Forensic Shot Analysis studies. Shot residues consist of partially burned and unburnt powder grains, gunpowder gas, capsule residues and inorganic and organic residues. As a result of determining the presence and density of shot residues on the target, the distance from which the shot was fired can be determined. The pattern and density of shot residues exhibit a direct correlation with the specifications of firearms and ammunition. The intended use and traits of the weapon affect the properties of the ammunition. An instance of specialised ammunition is subsonic cartridges which have lower powder burn rates and amounts compared to supersonic cartridges. To ensure accurate gunshot residue analysis, gunshot residue density and pattern from reference test-fires are necessary. The key factors affecting the GSR analysis are the type of weapon and ammunition used during test-fires, which should closely match those used in the incident. Any variation in these variables can reduce the precision of the residue analysis. In the study, an independent T-test was applied to determine whether there is a significant difference between the gunshot residue density on the target during test firing of 9×19mm diameter and type Supersonic and Subsonic cartridges with semi-automatic pistols at distances of 0cm, 15cm, 30cm, 60cm and 100cm. It was determined that a significant difference existed between supersonic and subsonic cartridges in the density and patterns of gunshot residue on the target resulting from shots fired at the mentioned distances.

Screen-printed electrode modified with bismuth film and chemometric techniques for on-site detection and classification of gunshot residues

The analysis of gunshot residues (GSR) is important for forensic science to help understand what happened in a crime scene. Many works on this have been published; however, there are a number of questions that remain. An analytical method should ideally respond to these questions: 1 Can the residue from a shooting or the analysis present a false positive? 2. Is it possible to identify the gun used in a shooting and information about it such as caliber and type of ammunition used? An analysis, as well, must be precise, easy to use, reproducible and allowable on-site. To achieve these requirements, voltammograms registered on a portable potentiostat, and chemometrics analysis were used. Electroanalytical techniques provide meaningful chemical information about a sample. Chemometric tools make it possible to build models to identify even small differences and respond to these questions with data. A total of 90 GSR samples were collected with the help of the Institute of Criminalistics in the state of Pernambuco, Brazil. The GSR were taken from 3 types of firearms, 2 of them with distinct ammunition. To assess the risk of false positives, 45 non-shooting samples were analyzed. The model constructed achieved a classification accuracy of 100 % to respond to the question of false positives. There was an accuracy rate of over 85 % for the second question, of identifying information about the weapon. A blind test was performed and used to prove that the electroanalytical-chemometrics methodology was useful and effective for GSR forensic investigators, enabling the emission of reliable reports, and contributing to faster processing of legal proceedings.

Pervasiveness of inorganic gunshot residue (IGSR) in handguns after cleaning and conditioning procedures.

Memory effect in firearms that is, the possibility for a weapon to release inorganic particles whose elemental composition depends on its entire shooting history, is responsible for most of the interpretation difficulties encountered in forensic gunshot residue analysis. The presence of residues chemically inconsistent with the last discharged round, the creation of particles having unusual elemental profiles, and the dependence of residue population composition on the collection point are all manifestations of memory effect. The experimental results reported in this paper highlight the ineffectiveness of a wide number of gun cleaning procedures in reducing memory effect. Moreover, the common alternative of discharging batches of rounds having a "new" primer mixture does not fully eliminate the possibility to recover "old" residues at least from the shooter's hands. Two brand new pistols and ammunition having lead-based, leadless and heavy metal free primers were used. Specimens, collected both from the shooters' hands and from cotton targets set nearby the gun muzzle, were analyzed by SEM-EDS and by ICP-OES. After discharging 10's of new ammunitions, the number of old residues ejected from the gun muzzle indeed showed an asymptotic decrease to zero. In spite of this, the number of old residues recovered from the shooter's hands did not follow any predictable trend. These different behaviors suggest that all internal components of a gun, and not just the barrel, play a role in memory effect.

Structural segregation in GSR from mercuric primers. A preliminary study

Since the second half of the XX century, primer mixtures based on mercury fulminate have become a rare occurrence on small ammunition markets in Western Europe and North America. As a consequence, Hg-containing gunshot residue (GSR) particles have not been as deeply investigated as residues from lead-based primer mixtures. As a matter of fact, no mention of GSR particles from mercuric primers is made by the current ASTM standard procedure for gunshot residue analysis. However, those laboratories dealing with ammunition and firearms produced in Eastern Europe or Asia still have a forensic interest in Hg-containing GSR. In this paper, a brief description of chemical composition and inner morphology of GSR particles from three different mercuric primers is reported. Regarding composition, arguments are given to promote SbSnHg residues to Characteristic of GSR particles when mercuric primers are discharged. From a morphological point of view, presence of inner nodules and other inhomogeneities were shown in GSR particles milled in a FIB/SEM. Moreover, mercury vaporization under the electron beam was observed for a particle reduced to a lamella. Mercury evanescence in GSR was interpreted in terms of mercury segregation during particle formation and higher mobility of Hg atoms in presence of defects (vacancies) in a strained lattice.

Assessment of gunshot residue detection on a large variety of surfaces by portable LIBS system for crime scene application

The application of Laser-Induced Breakdown Spectroscopy (LIBS) in forensic science has garnered increasing attention. The ability to perform real-time, on-site analysis of Gunshot Residue (GSR) particles and potential elements originating from bullets or projectile cores on various surfaces holds the potential to assist in resolving firearms-related cases. This includes facilitating trajectory determination by locating distinct impact points and identifying the types of ammunition used. This study evaluates the utilization of a portable LIBS device for ballistic forensic purposes. Additionally, it focuses on the assessment of potential false positives and false negatives arising from the different materials where the shots have been fired. Since the system performs laser ablation of both surface particles and the substrate, it emphasizes the importance of conducting preliminary screening in an area with the same composition as the impact zone to minimize potential false positives during direct surface analysis. Furthermore, the results demonstrate the capability to detect the constituent elements of characteristic gunshot residue particles (GSR particles): lead (Pb), antimony (Sb), and barium (Ba) adhering to bullets, as well as the principal elements composing the jacket or core of the projectile: lead (Pb), copper (Cu), and zinc (Zn) through direct analysis, without the need for a sampling kit, on different surfaces such as walls, furniture, or fabrics. Analyses conducted a month after the shots were fired indicate the potential for finding residues in the vicinity of the bullet hole. Analyses conducted a month after the shots were fired indicate the possibility of finding residues in the area around the bullet hole.

Determination of Al(III), Pb(II), and Cu(II) in Gunshot Residue Using Amino-Functionalized Silica Adsorbents in Dispersive Solid Phase Microextraction (DSPME) with Capillary Electrophoresis (CE)

Here is reported the design, synthesis, and application of an amino silica adsorbent for the extraction and determination of Al(III), Pb(II), and Cu(II) in gunshot residue (GSR) from the dorsal and palmar zones by capillary electrophoresis. The extraction procedure was used to determine the adsorbent composition by varying the molar ratio of the cross-linking agent tetramethyl orthosilicate (TMOS) and the functional monomer 3-aminopropyl trimethoxysilane (APTMS). (5.0:0.0 to 0.0:5.0). The optimal composition (3.0:2.0) was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and adsorption isotherm analysis. A univariate method was used to optimize critical factors in dispersive solid phase microextraction (DSPME), including the adsorbent mass, contact time, sample volume, and elution solution. Using the optimal conditions (adsorbent, 10 mg; contact time, 10 min; sample volume, 5 mL; eluent solution, methanol/10−1 mol L−1 HNO3), the method provides limits of detection of 0.06 mg L−1 for Pb(II), 0.08 mg L−1 for Cu(II), and 0.11 mg L−1 for Al(III). The precision and accuracy were evaluated in terms of inter- and intra-day repeatability (n = 3) with a relative standard deviation below 10%. The developed method was applied for gunshot residue analysis, providing concentrations from 12.6 to 702 mg L−1 for Al(III), 11.8 to 280 mg L−1 for Pb(II), and 29.8 to 395.6 mg L−1 for Cu(II).

Evolution of LIBS technology to mobile instrumentation for expediting firearm-related investigations at the laboratory and the crime scene

Gunshot residue (GSR) is one of the few forensic disciplines that lack accurate screening techniques. This study proposes using a mobile LIBS instrument to detect inorganic GSR and compares performance to a previously validated laboratory instrument. The mobile LIBS is designed with advanced configurations specifically for on-site GSR analysis, including a CMOS detector and a sampling chamber that holds up to six typical GSR collection devices with separate gas flow ports to prevent cross-contamination. A significant novelty of the portable instrument is its image magnification, which allows quick searching and visualization of GSR particle morphology. The single-particle imaging and elemental composition capability is one of a kind and offers superior confirmatory features for GSR. The mobile LIBS performance was evaluated for residues collected from the hands of shooters (100 samples) and non-shooters (200 background samples), analyzed sequentially by the mobile instrument and then the laboratory instrument. Accuracies better than 98.8% were obtained by both instruments, demonstrating their suitability for trace IGSR detection from skin specimens. Implementation of this methodology is anticipated to drastically speed up response times (i.e., from several hours per sample by standard SEM-EDS practice to a few minutes by LIBS). The screening methods can be easily incorporated into workflows to improve decision-making processes at the crime scene and laboratory settings, reduce backlogs, and improve case management.

Surgical mask as an alternative sampling site for gunshot residue analysis

Gunshot residue (GSR) has been identified in the oro-nasal cavities and in various areas of the face. However, there is no study in the literature about the outcome of the analysis if the mouth and nose are covered with a mask. The purpose of this study is to experimentally ascertain whether GSR detection can be made on surgical masks. Twelve civilians wearing facemasks were divided into six groups of two, each consisting of a shooter and an accompanying person. A single shot was fired by the mask wearing shooters of all six groups in an outdoor and indoor shooting range. The inner surface, outer surface, and strap of the mask were the three areas where we investigated for the presence of GSR. GSR particle counts of the shooter were higher than those of accompanying person. Analysis after outdoor range shootings yielded fewer particles than indoor range shootings. The most particles were detected on the outer surface of the masks, and the least on the inner surface. All analyzes performed on the shooters' mask revealed significantly higher number of particles compared to accompanying persons. The results showed a significant difference in the quantity of GSR particles identified, which could aid in distinguishing between the shooter and the accompanying person. The outer surface of the mask has been determined to be the most useful sampling location in this regard, as it is the sample where the difference is most prominent.

Development of a Dimensional Analysis Approach in Gunshot Residue Images Using Computerized Image Processing

Computer image processing is a method that uses artificial intelligence and machine learning-based general learning algorithms. With this method, objects in digital images (photos or videos) can be grouped by being perceived and detected. Computerized image processing method can be applied to almost all kinds of digital data produced with the developing technology. Nowadays, the identification and detection of gunshot residues (GSR) can be done manually by experts from the acquired images. In this study, computerized image processing method was used for the identification and dimensional analysis of gunshot residues (GSR). In this new proposed method, a dataset of 18500 digital image samples obtained from three different caliber cartridges (MKE, Gecco and S&B brands) was used. From the results of the study, it has been shown that the Computer Vision Method is a successful method in the automatic dimensional classification of GSRs.

The Nanoforensic: An Advanced Perspective in Crime Investigation

Nano forensics is the advanced application of nanotechnology-based techniques to resolve cases in forensic science. Forensic science offers scientific methods in a criminal investigation. Nano-forensics deals with the development of new approaches for fingerprint visualization, DNA isolation, forensic toxicology, explosive detection, identification of body fluids, gunshot residue analysis, detection of illicit drugs, etc. The nanomaterials used in forensic science are nanocrystals, nanoparticles, quantum dots, nanobelts, nanocomposites, nanoclusters, nanotubes, nanorods, etc. The scope of nanotechnology is very wide.

Lead isotope measurement of primer gunshot residues and likelihood ratio predictions for forensic cartridge discrimination and individualization in China

Gunshot residues (GSR), cartridge projectiles, and casings are frequently encountered evidence in gun-related forensic investigations. However, in circumstances where the investigation of striation marks is impossible, such as unrecovered or deformed projectiles and cartridge casings, GSR deposited on the hands or clothes of the shooter and victim-related items can provide information to establish a link between the suspect, the firearms used, and the victim. Since the formula of primers used by all cartridge manufacturers in China is identical, links based on the conventional morphological and compositional analysis of GSR are difficult to establish. However, the abundance of lead isotopes in primer components of lead styphnate varies significantly, and a fundamental understanding of these differences may facilitate the validation of primer (p)GSR evidence in forensic investigations. Here, 44 pGSR samples were characterized by Pb isotope ratios of 206 Pb/204 Pb, 207 Pb/204 Pb, and 208 Pb/204 Pb using laser ablation multicollector inductively coupled plasma mass spectrometry. There was no obvious mass fractionation of the lead isotope ratios of the primers from individual cartridges analyzed before and after the shooting process, thereby establishing a basis for the comparison of pGSR and unfired cartridges. Evaluation of the results using univariate likelihood ratio (LR) computations revealed low rates of misleading evidence (<0.53%) The results demonstrated that lead isotope ratio analysis of pGSR and LR predictions can provide a practicable method for forensic cartridge discrimination and individualization.

Identification and highly selective differentiation of organic gunshot residues utilizing their elemental and molecular signatures

Firearm related evidence is of great significance to forensic science. In recent years, many researchers have focused on exploring the probative value of organic gunshot residue (OGSR) evidence, which is often bolstered by many factors including recoverability. In addition, OGSR analysis has shown the potential to achieve differentiation between OGSRs generated from various ammunition brands and/or calibers. Raman spectroscopy is a vibrational spectroscopic technique which has been used in the past for gunshot residue analysis—including OGSR specifically. Raman spectroscopy is a nondestructive, highly-selective, simple, and rapid technique which provides molecular information about samples. LIBS or Laser-Induced Breakdown Spectroscopy is a simple, robust, and rapid analytical method which requires minimal to no sample preparation and a small amount of sample for analysis. LIBS provides information on the elemental compositions of samples.In this study, Raman spectroscopy and LIBS were used together in sequence in an attempt to achieve the specific identification and characterization of OGSR particles from ammunition types which were closely related. The main goal was to determine if this method had the potential to differentiate between various ammunition types of the same caliber and produced by the same manufacturer, and generated under identical firing conditions. High-resolution optical microscopy documented the OGSR particles’ morphologies and Raman spectroscopy was used to identify particles as OGSRs. Finally, LIBS analysis of the OGSR particles was carried out. Advanced chemometric techniques were shown to allow for very successful differentiation between the OGSR samples analyzed.

Experiences in successive forensic analysis of GSR and DNA traces collected on a single tape lift stub.

Gunshot residue (GSR) and deoxyribonucleic acid (DNA) analyses are used in the reconstruction of shooting incidents involving firearms. In both fields, adhesive tapes are commonly applied to recover traces. Using a simultaneous sampling approach for retrieving both types of traces from objects related to a shooting can be powerful. We present the results for DNA testing and GSR analysis using "DNA stubs" to recover both types of traces in one sampling. The analyses are successive: stubs are first examined with scanning electron microscopy for the presence of GSR and next subjected to DNA extraction and short tandem repeat (STR) typing. The results show no negative effect on the DNA and GSR results. The risk of DNA contamination during GSR analysis is addressed, showing that it is negligible. Our experiences in casework show that the approach can be successfully implemented.

Voltammetric Determination of New Chemical Markers in Gunshot Residues from Conventional and Ecological Ammunitions: Importance of Forensic Electroanalysis

Gunshot residues (GSR) are chemical traces present in the shooter's body. GSR are primarily deposited on the dorsal region of the hands. Metallic microparticles formed by Sb, Ba, and Pb are the main inorganic residues produced by conventional ammunition. These residues are commonly analyzed by SEM-EDS for forensic evidence. Currently, two experimental limitations for forensic GSR analysis exist: GSR (1) are produced indistinctly (revolvers, pistols, and shotguns, among other firearms, produce the same GSR.) and (2) are not produced when metal-free (ecological) ammunition is fired. To overcome the issue of absent metallic traces and to provide proper ammunition traceability, we suggest using luminescent chemical markers based on rare earth ions. These markers can be synthesized with different elements, to produce distinct colors depending on the firearm caliber. In addition, these markers present good visual detectability under forensic flashlights, and they can be detected and quantified by sensitive, low-cost instrumental techniques, such as voltammetry. In this context, we aimed to develop a composite containing Eu and Zr and to incorporate it in conventional and ecological ammunition propellants to test whether voltammetric detection of GSR traces collected after the shots is feasible.Conventional and ecological .380-caliber pistol ammunition was used. Both types of ammunition were previously disassembled with a commercial inertia hammer. Aliquots of the composite containing Eu and Zr were mixed at 10% ratio (w/w) with the propellants of these types of ammunition. Later, ammunition was reassembled with a mechanical press from Lee, model Lock Pro. The firing step was carried out in a professional shooting range; a .380 caliber pistol from Taurus, model PT 638 PRO, was used. Shots were fired on boards of pressed wood placed 1.0 m away from the end of the gun barrel. After the shooting stage, a Spectroline UV flashlight, model ENF-280C, was used to detect the luminescent chemical marker in the ammunition capsules and shot residues deposited on the hands, target, and weapon. GSR for SEM-EDS analysis were collected with aluminum stubs equipped with conductive adhesive tape. GSR aliquots for GC-MS analysis were collected by using swabs soaked with chromatographic grade ethanol solution and placed in 2.0-mL Eppendorf tubes. GSR aliquots for voltammetric analysis were collected by using carbon paste electrodes, with their surface being lightly pressed on the sample collection region.GSR detection by UV flashlight showed that the luminescent chemical marker was present on the target, hands, and weapon and in the deflagrated ammunition cases, as evidenced by red dots spread over the samples. This indicated that the method was practical, and that the luminescent chemical marker was effective for the intended purpose. Analysis of GSR from conventional and ecological cartridges by GC-MS showed that they had distinct chemical profile, but the chemical components present in the luminescent chemical marker could not be detected. MEV-EDS analysis allowed particles containing the luminescent chemical marker to be detected in the cases of GSR from conventional and ecological munitions. The characteristic peaks of Zr and Eu were observed during EDS analysis, indicating that this technique can also be used to detect these markers. The voltammetric results indicated that the luminescent chemical marker can be detected through Zr detection at an anodic peak potential of 0.45 V vs. Ag/AgCl, consistent with the expected signal for this element. Additional substances present in these residues did not interfere in voltammetric Zr detection, making the new methodology a fast and viable alternative for forensic analysis. Figure 1

A likelihood-ratio framework for evaluating results of forensic gunshot-residue analysis

When reporting results of Gunshot Residue (GSR) analysis from a person suspected to be involved in a recent shooting, most forensic experts only provide the court with the raw results (i.e. the number of GSR particles found) and a disclaimer that a positive finding does not prove that the suspect was involved in a firearm shooting incident whilst a negative finding does not prove that he was not. Probabilistic analysis of the GSR results provides more value to the court, so the present study calculated likelihood ratio (LR) values for finding 0–8 characteristic GSR particles (containing Lead, Barium and Antimony) on a suspect's hands, based on the available GSR data from the published literature as well as studies by the authors. Defense propositions, i.e. modes for GSR acquisition other than involvement in a shooting event, were divided into three broad categories: low, medium and heavy background. For each background level and number of GSR particles found, minimal and maximal LR values were calculated. Thus, for each proposition the defense provides for the presence of GSR on the defendant's hands, the forensic expert can provide a possible set of minimal and maximal LR values, leaving the court to examine the defendant's contention and decide which of the three background modes is more plausible according to the circumstances of the specific case.

Analysis of gunshot residues from nontoxic ammunition: a contribution to health and environmental analysis

This study’s aim was to determine the presence, as well as to evaluate the health and environmental impacts, of chemical elements from firearm shots during shooter practice at outdoor shooting ranges, both in the environment and on the shooters’ hands. Two high-precision devices were used for measuring suspended particles that are released during discharge of Taurus PT 100 .40 caliber pistols. The analysis of collected data allowed the identification of specific distribution patterns of samples that were adsorbed. Moreover, samples were collected from the opisthenar area of the hand to investigate both the occurrence and deposition of particles and chemical elements through scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The results indicate that copper, lead, and zinc concentration profiles will be able to delimit and reveal more precise details regarding shots made with nontoxic ammunition (NTA). In particular, the residual graphic analysis indicated that the majority of metal deposited in the shooter's hand is zinc. Further, the metals barium and lead also were detected. Due to the exposure to these elements, it could be concluded that engineering controls and administrative management should be sought in order to avoid human overexposure and environmental release of these airborne toxic metals.