Characterisation of gunshot residues from non-toxic ammunition and their persistence on the shooter’s hands

Investigating gunshot wounds in charred bone with XRF spectroscopy: a technical note

The analysis of traces of injuries can be difficult in cases of charred human remains since the alteration and fragmentation are high. The aim of this study is to explore the use of X-Ray Fluorescence (XRF) technique as a screening tool for detecting and analyzing gunshot residues (GSR) on cremated and highly fragmented materials, as it is a technique that allows for fast qualitative investigations without altering the sample or requiring sample preparation. The study was carried out on two steps: firstly, on completed skeletonized bones to verify if GSR survive to burning; secondly, we considered a more realistic situation, in which soft tissues were present before the shooting. To this aim, nine adult bovine ribs, four retaining soft tissue, five completely skeletonized, were subjected to a shooting test using two types of 9 mm projectiles (jacketed and unjacketed bullets). The ribs were then burnt until complete calcination in an electric furnace. The entry wound of each rib was analyzed using XRF, revealing traces of GSR. The XRF analysis showed that all samples, except for one, contain Pb and/or Sb near the lesion. Furthermore, the samples hit by unjacketed bullets had a more significant presence of Pb in macroscopic yellow areas, which persisted when moving away from the gunshot. These findings could pave the way for the use of XRF technology, mostly when a fast and immediate scan must be done on osteologic materials by a conservative method.

Exploring particle populations of common inorganic gunshot residue interferences through single particle inductively coupled plasma time-of-flight mass spectrometry

Inorganic gunshot residue (IGSR) has certain environmental and occupational interferent-particle sources known to display similar morphologies and elemental compositions to IGSR. These interferences can make detecting and identifying IGSR particles difficult, especially when IGSR particle number concentrations are low. Here, single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) is used to explore the particle types measured from IGSR and three important interferent-particle sources: brake pads, fireworks, and mineral sunscreen. spICP-TOFMS offers results in as little as 2 min per sample. With spICP-TOFMS, the mass of most elements, down to the 10s of attograms, can be detected and quantified in individual particles with diameters from 10s to 100s of nm. At this size range, almost all interferent sources produce particles with elemental compositions that overlap with ASTM-defined particle compositions used for identifying leaded and lead-free IGSR. We establish probabilities for detecting IGSR-like particles from interference sources through the analysis of thousands of particles from each interference. Based on this analysis, robust sample-specific 'characteristic' particle types can be used to classify leaded and unleaded IGSR particles, even in the presence of interferent particles. Of the interference sources studied, particles from brake pads and fireworks are most similar to leaded IGSR; however, IGSR particles could be unequivocally classified based on detection of lead and antimony. Particles from mineral sunscreen are most similar to those from lead-free IGSR; however, lead-free IGSR particles exhibit a unique titanium-zinc-copper elemental fingerprint that is not detected in mineral sunscreen particles. Within mixtures of interference particles and IGSR, IGSR is accurately identified with limited false positives, even when the number of interference particles is over 200-times greater than that of IGSR. Our results suggest that spICP-TOFMS is a useful approach for rapid and accurate IGSR identification even in samples with high concentrations of interferent background particles.

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.

Assessing the shooting distance of lead-free ammunition regardless of composition using Laser Induced Breakdown Spectroscopy

At present, it is challenging to accurately determine firearm shooting distances in the case that lead-free ammunition is involved, largely because different manufacturers use different primer compositions. Laser-induced breakdown spectroscopy (LIBS) allows the simultaneous detection of multiple elements with high sensitivity and so may represent a solution to this problem. Previous studies have, in fact, demonstrated that LIBS can be used to determine shooting distances when working with gunshot residues from conventional ammunition based on scanning fabric surfaces. The present study confirms that the shooting distance can be ascertained using LIBS to detect copper originating from the ammunition casing and projectile but not the primer on fabric surfaces. This estimation can be performed regardless of the primer composition of lead-free ammunition.

Key points

Evaluation of gunshot residue from lead-free ammunition using scanning electron microscopy-energy dispersive X-ray analysis indicated that 40% of the particles contained copper.The iForenLIBS system allowed the detection of copper-containing particles on fabric surfaces after firing at different distances with high sensitivity.Laser-induced breakdown spectroscopy can determine the shooting distance of lead-free ammunition through copper detection even in ammunition that does not used this element in the primer.This technique can generate density maps allowing the evaluation of short, medium, and long-range shooting distances.

Divergent gunshot residues and characterization of the memory effect in a .22 caliber revolver and pistol

Background

The forms and compositions of primer gunshot residue (GSR) in shooting cases have been routinely analyzed in many crime labs by scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS). Gunshot residue studies over the last 30 years have identified a contribution by residual GSR from surfaces within the firearm to GSR (the “memory effect”). In this study, we first focus on the GSR compositional differences between target, bore, and cylinder gap for a .22 caliber revolver which has received little attention in the literature. Secondly, we examine the behavior of elements involved in the residual contribution to GSR for a .22 caliber pistol.

Results

The compositions of target, bore, and cylinder gap GSRs from a .22 caliber revolver were determined for 11 discharge series. Breech GSR compositions from a .22 caliber pistol changed in sequential discharges revealing behavior of individual primer and bullet elements. The target GSR forms from some .22 caliber ammunitions were not spherical.

Conclusions

For the revolver, GSR compositions from the target, bore, and cylinder gap are divergent. Analysis of the pistol’s breech GSRs indicated mixing with the previously deposited GSRs resulting in a sequential contribution or loss of elements and redeposition of the new composition. Aluminum did not contribute to the residual GSR. The GSR composition of a discharge and its contribution to residual GSR on the internal parts of the firearm represents a complex process which likely involves a number of variables including, but not restricted to firearm design, primer composition, pressure and temperature of the discharge gas, and bullet surface composition.

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.

Airborne and Dermal Collection Methods of Gunshot Residue for Toxicity Studies

Gunshot residue (GSR) has potential negative health effects on humans as a result of inhalation and dermal exposure to the chemical and physical characteristics of GSR such as Pb, Sb, Ba, nitrocellulose, nitroglycerine, and particulate size fraction. Filter (size selective) and double-sided tape (non-size selective) samples collected airborne GSR during single and triple firing of a 0.22 caliber revolver. Dermal exposures were considered using hand swabs and de-leading wipes, designed to remove the heavy metals. The samples underwent analysis to investigate physical (morphology, size distribution, zeta potential), chemical (black carbon and element concentrations), and potential to induce oxidative stress (oxidative potential via the dithiothreitol (DTT) assay). All sample types detected Pb concentrations higher than national ambient air standards. The de-leading wipes reduced the metal content on the hands of the shooter for Pb (15.57 ± 12.99 ppb and 3.13 ± 4.95 ppb). Filter samples provided health relevant data for airborne PM2.5 for all of the analysis methods except for GSR morphology. This work identified collection and analysis methods for GSR in an outdoor setting, providing protocols and considerations for future toxicological studies related to inhalation and dermal exposures to particulate GSR. Future studies should investigate the influence of meteorological factors on GSR exposure in an outdoor setting.

Strontium in barium sulphate as a discriminating factor in the forensic analysis of tool paint by SEM/EDS

In the context of forensic tool paint analysis, the development of analytical strategies to distinguish between different tools is of great interest in order to form a better opinion on whether or not a trace of paint seized at a crime scene originates from a tool found, for example, during a search of a house. A study was therefore conducted on the potential of using X-ray mapping to discriminate red tools that are not otherwise distinguished by standard analytical techniques (i.e. optical microscopy, infra-red spectroscopy, Raman spectroscopy). In this study, the presence of trace amounts of strontium - revealed by X-ray mapping - in the main mineral filler, namely barium sulphate, allowed the discrimination of different tools using a statistical approach. This study is one example among others of the potential of X-ray mapping for a better characterisation of tool paints in a forensic context.

Molybdenum in Gunshot Residue: Experimental Evidences and Detection Challenges in the Presence of Lead and Sulfur

Inorganic gunshot residue (GSR) analysis is carried out by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) in many forensic laboratories. Characteristic GSR often consists of lead–barium–antimony, commonly associated with sulfur. The strength of forensic GSR evidence increases when unusual elements are found in residues collected both from the suspect and from the discharged firearm. The presence of molybdenum in GSR, due to the use of MoS2 lubricants in firearms, is experimentally demonstrated here for the first time. The most intense molybdenum X-ray emissions are MoL peaks at 2.3 keV which overlap with PbM and SK families due to the poor resolution of EDS detectors. When Pb, S, and Mo are allegedly present in the same particle, the reliability of automatic EDS routines is at risk. Missing identifications or false detections and exclusions may then occur. Molybdenum should be considered as detected only if MoK emissions meet the peak-to-background ratio minimum requirements. A strategy to spot Mo-containing residues is described, based on the automated search of MoS2, using a new “Sulfur only” class added to the classification scheme, followed by careful manual review of all GSR particles at an acceleration voltage of 30 kV. Our proposal improves commonly adopted forensic procedures currently followed in casework.

A study of the effect of working parameters and validation of SEM/EDS method for determination of elemental composition of commonly encountered GSR samples in shooting events in Kosovo

Reliability of forensic evidences for presence of inorganic gunshot residue (iGSR) on a given surface strongly depends on the performance of scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) method. This article presents the results from a study of the effect of SEM/EDS working parameters on the method performance and quality of iGSR data, as well as a development of a database of iGSR encountered in R Kosovo. The optimal working parameters of SEM/EDS were established by one-variable-at-a-time approach and the method was validated according to ASTM1588-10. The precision, trueness, and expanded uncertainty for PbBaSb particles were estimated and the method was assessed as a "fit for purpose" with a satisfactory performance (z-score < 2). Expended uncertainty of quantification of GSR particles estimated by single laboratory and quality control approach was 6% (k = 2). The validated SEM/EDS method was applied for identification of characteristic iGSR particles in samples from shooting events in Kosovo. The method was demonstrated to be capable of providing a legal proof for iGSR existence on a specific surface. The quality of the results was not influenced by the origin of iGSR. Five hundred fifty-five samples from 144 cases occurred during the last 3 years were analyzed and 14% rate of positive results was found.

Gunshot residue detection technologies—a review

Background

Gunshot residue (GSR) is a shred of important trace evidence which helps forensic scientists solve a huge range of incidents related to firearms. The identification of the shooter to bullet identification from a gunshot wound help reconstruct a scene of the crime.

Main body

The review of this scientific paper is based on gunshot residue, its composition, and the growing advanced technology which allow us to study about how GSR analysis help to identify and detect residues. Various methods are acquired to identify and analyze organic and inorganic residues present when ammunition is fired. The review highlights the composition of GSR, its collection methods, and analysis part which emphasize on all the methods developed so far. The use of conventional methods including colorimetric and instrumentation-based analysis and advanced technology including electrochemical technique for detecting residues from the last 50 years. Spot tests or chemical tests were performed but they degrade the sample and can sometimes cause hindrance with some other nearby material present at the crime scene. Instrumentation techniques including AAS, ICP-MS, SEM, SEM-EDX, GC, HPLC, etc. are discussed in detail. Mostly advanced electrochemical methods developed are for inorganic gunshot residues (IGSR), but some researchers worked on both residues. Also, the fabricated electrochemical cells are replaced by a single strip-based technique for easy detection. So, to combat these issues, various scientists are moving towards sensor-based methods for rapid and reliable detection. These methods are more user-friendly, sensitive, and cost-effective and provide rapid detection results.

Conclusions

This review results in the composition of GSR, its collection methods, and analysis using sophisticated methods that emphasize all the methods developed so far and it also culminates the merits and demerits of all detection methods.