A Novel LIBS Sensor for Sample Examinations on a Crime Scene.

In this work, we present a compact LIBS sensor developed for characterization of samples on a crime scene following requirements of law enforcement agencies involved in the project. The sensor operates both in a tabletop mode, for aside measurements of swabbed materials or taken fragments, and in handheld mode where the sensor head is pointed directly on targets at the scene. The sensor head is connected via an umbilical to an instrument box that could be battery-powered and contains also a color camera for sample visualization, illumination LEDs, and pointing system for placing the target in focus. Here we describe the sensor's architecture and functionalities, the optimization of the acquisition parameters, and the results of some LIBS measurements. On nano-plotted traces at silica wafer and in optimized conditions, for most of the elements the detection limits, in term of the absolute element masses, were found to be below 10 picograms. We also show results obtained on some representative materials, like fingerprints, swabbed soil and gunshot residue, varnishes on metal, and coated plastics. The last, solid samples were used to evaluate the depth profiling capabilities of the instrument, where the recognition of all four car paint layers was achieved.

Chemical Analysis of Gunpowder and Gunshot Residues.

The identification of firearms is of paramount importance for investigating crimes involving firearms, as it establishes the link between a particular firearm and firearm-related elements found at a crime scene, such as projectiles and cartridge cases. This identification relies on the visual comparison of such elements against reference samples from suspect firearms or those existing in databases. Whenever this approach is not possible, the chemical analysis of the gunpowder and gunshot residue can provide additional information that may assist in establishing a link between samples retrieved at a crime scene and those from a suspect or in the identification of the corresponding model and manufacturer of the ammunition used. The most commonly used method for the chemical analysis of gunshot residue is scanning electron microscopy with energy dispersive X-ray, which focuses on the inorganic elements present in ammunition formulation, particularly heavy metals. However, a change in the legal paradigm is pushing changes in these formulations to remove heavy metals due to their potential for environmental contamination and the health hazards they represent. For this reason, the importance of the analysis of organic compounds is leading to the adoption of a different set of analytical methodologies, mostly based on spectroscopy and chromatography. This manuscript reviews the constitution of primer and gunpowder formulations and the analytical methods currently used for detecting, characterising, and identifying their compounds. In addition, this contribution also explores how the information provided by these methodologies can be used in ammunition identification and how it is driving the development of novel applications within forensic ballistics.

[Current approaches for sampling to study the traces of gunshot residue]. / Sovremennye podkhody k otboru prob dlya issledovaniya sledov produktov vystrela.

An overview of researches, mainly by foreign specialists, on current available approaches for sampling to study the traces of gunshot residue (GSR) is presented. The comparative characteristics of traditional methods of samples (use of cotton and gauze tampons, blotting paper, textile fabrics, adhesive tapes, adhesives and vacuum samplers), as well as advanced technologies, including special devices and sorbents, are given. The characteristics of samplings from hands, scalp, nostrils, clothes of examined persons as well as procedures, that allow to increase the duration of GSR detection, are described in details. The importance of GSR sustainability over time is noted. On average, the most likely detection periods of particles are less than 1 hour for samples, collected from hands, more than 1 hour for samples from clothes and 2-3 hours for face. It is possible to detect the GSR particles in hair up to 24 h., and in nasal mucus after 6 h. of shot. The methods of identification and determination for analytes of inorganic and organic nature are discussed. The most common methods for determining heavy metal particles are atomic spectrometry, namely atomic absorption with electrothermal atomization and atomic emission. The combination of scanning laser ablation and mass-spectrometry with inductively coupled plasma makes it possible to detect more than 15 analytes in a single sample. Scanning electron microscopy with X-ray detectors is effective for the examination of powder particles. The described methods of sampling complement each other increasing the possibility of evidence base for court proceedings.

Comparison of four commercial solid-phase micro-extraction (SPME) fibres for the headspace characterisation and profiling of gunshot exhausts in spent cartridge casings.

Headspace solid-phase micro-extraction (SPME) is a promising technique for the characterisation and profiling of gunshot exhausts in spent cartridge casings, especially for health and environmental risk assessments, as well as forensic purposes. To date, however, no comprehensive investigation has been carried out to objectively assess the kinds of compound released during a discharge that can be recovered by this approach, the selectivity of the main commercially available fibres, and their relative performances for the analysis of gunshot exhausts and the discrimination of different ammunition types. This study aimed to fill this gap. Gunshot exhausts in spent cartridge casings from four different ammunition types were analysed by GC-MS, after extraction with four different commercial fibres: 100 µm polydimethylsiloxane (PDMS), 85 µm polyacrylate (PA), 65 µm polydimethylsiloxane/divinylbenzene (DVB), and 85 µm carboxen/polydimethylsiloxane (CAR). Results showed that, overall, a total of 120 analytes could be observed across the cartridges, but the different tested fibres also displayed distinct performances, which were, to some extent, complementary for the characterisation of gunshot exhausts. DVB, in particular, recovered the most compounds simultaneously. On the other hand, the observed variability between measurements was also high, making it a poor candidate for (semi-)quantitative applications (e.g. estimation of time since discharge and/or source profiling). In this regard, PA demonstrated the highest potential for broad use and implementation in multi-purpose methods.

Lead toxicity in Lucilia cuprina and electrochemical analysis: a simple and low-cost alternative for forensic investigation.

Entomotoxicology allows the detection and analysis of substances such as poisons, drugs, and metals in necrophagous insects using analytical protocols. In a forensic situation related to death by gunshot, the gunshot residue (GSR) is dispersed at the crime scene and may be consumed by necrophagous insects. Lead (Pb) is the most abundant metal in GSR samples and it can be determined using non-portable methods. However, the toxicity effects of GSR samples on Lucilia cuprina (Diptera: Calliphoridae) and the detection of Pb via portable electrochemical methods have not been investigated. This study describes for the first time the toxicity analysis of Pb on immature L. cuprina through their survival rate and influence of Pb on immature development. In addition, the bioaccumulation of Pb in the larvae samples was determined based on square wave anodic stripping voltammetry (SWASV) measurements. The results revealed a low limit of detection to Pb (6.5 µg L-1) and the analytical performance was satisfactory because it measures Pb levels in larvae exposed to a diet containing 50 µg Pb g-1. Furthermore, the levels of Pb influenced the survival rate and development time of the immature L. cuprina. Larvae exposed to a high concentration of the metal (50 µg Pb g -1) showed statistically significant changes (p < 0.05). The presence of Pb in immature L. cuprina can be used to estimate the post-mortem interval; thus, the present study provides important information in forensic entomology.

Advances and limitations in the determination and assessment of gunshot residue in the environment.

Gunshot residue (GSR) stemming from the discharge of firearms has been essential to advancements in the field of forensic science however the human and environmental health impacts from GSR are far less researched. GSR represents a multifaceted concern: it contains a complex mixture of inorganic and organic components and produces airborne particles with variable sizes, depositions, and fates. Herein we evaluate studies in the literature examining GSR collection, deposition, composition, environmental contamination, and potential remediation techniques within the last two decades (2000 - 2020). Throughout we reflect upon key findings and weaknesses in relation to environmental characterization of GSR and associated firearm contaminants. Research focused on techniques to analyze both inorganic and organic GSR simultaneously has begun, but requires additional effort. A vast majority of the available environmental characterization literature focuses on soil contamination at outdoor firing ranges for a select number of elements (Cu, Pb, Sb) with comparisons between ranges or at different collection distances and depths. There is limited ability for between study comparisons due to collection and analysis differences as well as a lack of background soil sampling. Notably, these studies lack direct quantification of the contribution of contaminants from GSR as well as analysis of organic compounds. Currently, there is a need for air monitoring to determine the composition, deposition, and fate of GSR, particularly in outdoor settings. This review summarizes the collection, characterization, and environmental studies related to GSR and highlights areas of research needed to establish the environmental health impacts.

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 lead­barium­antimony, 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.

Technical note: presence of gunshot residue in and around a police station.

Previous studies on the transference of gunshot residue (GSR) have shown that GSR can be transferred to surfaces through everyday activities and can persist on surfaces. Being that all police departments operate differently and have different spaces, GSR can be transferred and accumulates in different areas. Samples were collected from persons and surfaces in and around the Scranton Police Department and tested by scanning electron microscopy to identify GSR. Surfaces included police car seats, gun holsters, clothing around holsters, and belts around holsters. The results of the study showed that of the 25 samples collected, 40% contained at least one particle that was "characteristic of primer GSR", 64% contained at least one particle that was "consistent with primer GSR", and 92% contained at least one particle considered "commonly associated with primer GSR". This research characterizes where GSR is transferred within and around the police department. This data can be used to implement cleaning procedures or methods for decontamination. This study continues to strengthen the body of knowledge surrounding transferring of GSR.

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

The aim of this work was to characterise three non-toxic ammunition (NTA) from the GECO and Fiocchi brands, which are available in the Italian market. Characterisation was carried out by considering both the elemental chemical composition and morphology, using scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDS). Particles were collected from both the cartridge cases and the shooters' hands after shooting tests. Six volunteers fired two shots for each ammunition. Several elements, such as aluminium, potassium, silicon, sulphur, titanium and zinc were found in gunshot residue (GSR) particles from different ammunition. We also studied the persistence of these types of GSR on the hands of the shooters in a range between 1 and 6 h after shooting. The GSR particles from the three NTA tested were found on the hands of shooters until 6 h after the shots. The characterisations undertaken in this work will be useful for specialists in forensic science and legal medicine to evaluate trace evidence from these new NTA in casework, as such formulations are in growth.

Gunshot residue on dark materials: a comparison between infrared photography and the use of an alternative light source.

The pattern of gunshot residue (GSR) includes important information about muzzle-target distance since a larger GSR distribution diameter indicates a larger shooting distance. GSR may not be visible to the naked eye when, for example, it is located on dark textiles. In such cases, further procedures need to be performed in order to visualize the pattern of GSR. Besides chemical procedures, an alternative light source or infrared photography can be utilized for non-destructive GSR visualization. In the work presented, these two techniques are compared based on shooting experiments using 26 different dark textiles. Within the range of the alternative light source, the use of a 440-nm light in combination with an orange-colored filter led to the best visualization of GSR in the form of fluorescent particles. Infrared photography, on the other hand, visualized GSR as dark particles, whereas-ideally-the dark textile reflected the infrared light and appeared bright. The comparison of both techniques revealed that the GSR distribution visualized by infrared photography was not identical to the GSR distribution visualized with 440-nm illumination in combination with an orange-colored filter. We concluded that infrared photography visualizes the inner powder soot zone, whereas illumination at 440 nm leads to fluorescence of the outer powder soot zone, which can be visualized using an orange-colored filter. Knowledge of this difference in visualization of the two powder soot zones is important for forensic practitioners assessing firing distances. In the literature, however, this difference is not noted as clearly.

Unusual sources of Sn in GSR. An experimental study by SEM and IBA.

Gunshot Residue (GSR) produced by the discharge of a firearm often provides very useful information in criminal investigations in cases involving the use of firearms. Scanning Electron Microscopy equipped with an Energy Dispersive X-ray Spectrometer (SEM-EDS) is typically used worldwide to visualize micrometric particles constituting GSR and to analyse their elemental composition. The 2017 ASTM Standard guide for gunshot residue analysis by scanning electron microscopy/energy dispersive X-ray spectroscopy specifies that "Particles classified as characteristic of GSR will have one of the following elemental compositions: Lead, antimony, barium; Lead, barium, calcium, silicon, tin". For the first time, the presence of an additional element, such as Sn, plays a key role in ASTM particle classification. It is known that some ammunitions, used for pistols, revolvers and rifles, contain tin foil discs for sealing the primer mixture into the cup, resulting in GSR particles containing Sn. The authors faced some cases in which Sn was unexpectedly found in GSR particles from a 0.22 Long Rifle derringer and from some 12 gauge shotguns. No tin foil discs are used in rimfire ammunitions and there is no published evidence of tin foil discs in shotshell ammunitions. Following a "case by case" approach, experimental research has been carried out to explain how Sn can be present in GSR particles when the last discharged cartridge also does not contain any Sn either in components and in the explosive charges. Moreover, the use of Particle Induced X-ray Emission (PIXE) showed the capability to overcome overlap ambiguity of Sb and Sn peaks in the X-ray spectra, being a possible key issue in real shooting cases if Sn quantities are below the lower limit of SEM detection, especially when Sb is also present.

Raman microspectroscopic mapping as a tool for detection of gunshot residue on adhesive tape.

Our research group previously reported a novel method for the detection of gunshot residue (GSR) via tape lifting combined with Raman microspectroscopic mapping and multivariate analysis. This initial study achieved proof of concept for this approach. Here, we report validation studies which investigate the reproducibility/ruggedness and specificity of the approach. Raman mapping for GSR detection on adhesive tape was performed on an independent Raman microscope, not used to generate the training set. These independent spectra were classified against the original training dataset using support vector machine discriminant analysis (SVM-DA). The resulting classification rates of 100% illustrate the reproducibility of the technique, its independence upon a specific instrument and provide an external validation for the approach. Additionally, the same procedure for GSR collection (tape lifting) was performed to collect samples from environmental sources, which could potentially provide false-positive assignments for current GSR analysis techniques. Thus, particles associated with automotive mechanics were collected. Automotive brake and tire materials are often composed of the heavy metals lead, barium, and antimony, which are the key elements targeted by current GSR detection technique. It was determined that Raman spectroscopic analysis was not susceptible to misclassifications from these samples. Results from these validation experiments illustrate the great potential of Raman microspectroscopic mapping used with tape lifting as a viable complimentary tool to current methodologies for GSR detection. Furthermore, current methodologies are not well-developed for automated organic GSR detection. Illustrated here, Raman microscoptrosocpic mapping has the potential for the automatic identification of organic GSR. Graphical abstract ᅟ.

Trends in analysis of gunshot residue for forensic purposes.

Detection and identification of organic and inorganic components of gunshot residue are well established within forensic chemistry because of highly characteristic and uncommon features of the products of ammunition discharge at the time and place of a shooting incident in comparison to other materials present in daily life of people. Both types of residue play an important role in establishing various circumstances of a shooting crime, though the most vital one concerns the possibility of relating a suspect with the activity of shooting. In this aspect, solid, inorganic particles, nowadays called characteristic, have been utilized. Their specific features result from the primer mixture composition, including compounds of heavy metals, lead, antimony, and barium, and from the extraordinarily dynamic conditions of their formation, taking place at the moment of the primer detonation. Scanning electron microscopy and X-ray microanalysis techniques proved to be necessary and sufficient to reveal the content and the spherical morphology of the particles for this purpose. Recently, the recommendation that the potential for lead exposure be minimized was followed in the production of ammunition cal. 9 mm Luger, 0.40 S&W, 0.380 Auto, and 0.38 Special. These modern types of ammunition expel less characteristic particles, the identification of which can be a challenge for the examiners. At least two solutions to strengthen the residue identity are taken into account: additional insights into the internal structure of inorganic particles, e.g., by means of electron backscattered diffraction and focused ion beam, as well as complementary examinations of organic residues with sensitive mass spectrometric techniques.

A study of gunshot residue distribution for close-range shots with a silenced gun using optical and scanning electron microscopy, X-ray microanalysis and infrared spectroscopy.

Detailed physical and chemical analysis of gunshot residue deposited in the nearest vicinity of a submachine gun alone and with a sound suppressor was performed. The studies were inspired by recent shooting cases with the use of a firearm with a silencer and the need to estimate the shooting distance to human body naked and covered with clothing. A series of experiments were performed in the shooting range using a machine pistol and the appropriate ammunition cal. 7.65mm Browning. Targets were placed in the range of 0-30cm from the gun and covered either with white cotton fabric or a porcine skin that mocked people's clothing and the naked skin. Both the organic and inorganic residue were examined by means of optical microscopy, infrared spectrometry as well as scanning electron microscopy and energy dispersive X-ray spectrometry. The influence of factors, such as sound suppressor, shooting distance and the substrate type on the mechanism of particles spread and their availability for research was established and discussed.

Micro-CT features of intermediate gunshot wounds covered by textiles.

The analysis of gunshot residue (GSR) on the clothing and the underlying skin of the victim may play an important role in the reconstruction of the shooting incident. The aim of the present study was to test micro-computed tomography (micro-CT) for the analysis of firearm wounds experimentally produced on human skin covered by textiles. Firing trials were performed on 60 sections of human calves enveloped by a single layer of fabric (cotton or jeans or leather or nylon) and 15 controls consisting of bare calves. Experimental firings were conducted in a ballistic laboratory at three different muzzle-to-target distances (5, 15, and 30 cm), using a .32 ACP pistol (Beretta Mod. 81) loaded with full-jacketed bullets coming from the same production lot (7.65 × 17 mm, Browning SR). The visual inspection revealed the classic pattern of GSR distribution on the fabrics and the skin of control samples, while only a dark ring around the entrance lesion was identified on the skin beneath the fabrics. Micro-CT analysis showed the presence of radiopaque material on all entrance wounds, with a statistically significant difference between cases and controls. No differences were found among specimens covered by fabrics, with regard to the firing distance and the type of clothing. No GSR-like deposits were detected in exit wounds. Our results suggest that micro-CT analysis may be a useful screening tool for differentiating entry from exit gunshot wounds when the covering textiles are contaminated, damaged, or missing.

Surface-enhanced Raman spectroscopy for the analysis of smokeless gunpowders and macroscopic gunshot residues.

Gunshot residues (GSR) result from the discharge of a firearm being a potential piece of evidence in criminal investigations. The macroscopic GSR particles are basically formed by burned and non-burned gunpowder. Motivated by the demand of trace analysis of these samples, in this paper, the use of surface-enhanced Raman scattering (SERS) was evaluated for the analysis of gunpowders and macroscopic GSR particles. Twenty-one different smokeless gunpowders were extracted with ethanol. SERS spectra were obtained from the diluted extracts using gold nanoaggregates and an excitation wavelength of 633 nm. They show mainly bands that could be assigned to the stabilizers diphenylamine and ethylcentralite present in the gunpowders. Then, macroscopic GSR particles obtained after firing two different ammunition cartridges on clothing were also measured using the same procedure. SERS allowed the detection of the particles collected with an aluminum stub from cloth targets without interferences from the adhesive carbon. The results demonstrate the great potential of SERS for the analysis of macroscopic GSR particles. Furthermore, they indicate that the grain-to-grain inhomogeneity of the gunpowders needs to be considered. Graphical Abstract SERS allows the detection of GSR particles collected with adhesive stubs from cloth targets using gold nanoaggregates and an excitation wavelength of 633 nm.

Preliminary classification of characteristic organic gunshot residue compounds.

For the first time, a classification system for organic gunshot residue (OGSR) compounds with respect to the confirmation of OGSR materials is presented. There are 136 compounds considered to be associated with OGSR that have been highlighted in the literature. Many of these compounds could be classified as being ubiquitous in the environment and thus their detection as characteristic components of OGSR could cause issues with the interpretation of chemical ballistic evidence. The proposed system aims to address this problem by classifying OGSR compounds based on their forensic relevance with respect to the confirmation of GSR materials. To increase the forensic relevance of such a system, the large number of OGSR compounds reported in the literature has been decreased to 20 OGSR compounds based on the organic chemical composition of over 200 propellant powders. Occupational and environmental materials also associated with OGSR compounds have been considered.

Fast detection and characterization of organic and inorganic gunshot residues on the hands of suspects by CMV-GC-MS and LIBS.

A rapid method for the characterization of both organic and inorganic components of gunshot residues (GSR) is proposed as an alternative tool to facilitate the identification of a suspected shooter. In this study, two fast screening methods were developed and optimized for the detection of organic compounds and inorganic components indicative of GSR presence on the hands of shooters and non-shooters. The proposed methods consist of headspace extraction of volatile organic compounds using a capillary microextraction of volatiles (CMV) device previously reported as a high-efficiency sampler followed by detection by GC-MS. This novel sampling technique has the potential to yield fast results (<2min sampling) and high sensitivity capable of detecting 3ng of diphenylamine (DPA) and 8ng of nitroglycerine (NG). Direct analysis of the headspace of over 50 swabs collected from the hands of suspected shooters (and non-shooters) provides information regarding VOCs present on their hands. In addition, a fast laser induced breakdown spectroscopy (LIBS) screening method for the detection of the inorganic components indicative of the presence of GSR (Sb, Pb and Ba) is described. The sampling method for the inorganics consists of liquid extraction of the target elements from the same cotton swabs (previously analyzed for VOCs) and an additional 30 swab samples followed by spiking 1µL of the extract solution onto a Teflon disk and then analyzed by LIBS. Advantages of LIBS include fast analysis (~12s per sample) and high selectivity and sensitivity, with expected LODs 0.1-18ng for each of the target elements after sampling. The analytical performance of the LIBS method is also compared to previously reported methods (inductively coupled plasma-optical emission spectroscopy). The combination of fast CMV sampling, unambiguous organic compound identification with GC-MS and fast LIBS analysis provides the basis for a new comprehensive screening method for GSR.

Prevalence of gunshot residue particles on back seats of police vehicles.

The presence of gunshot residue (GSR) in a sample can provide valuable information in forensic investigations by associating a suspect with a shooting incident. However, in order to have confidence in the integrity of the results' interpretation, the possibility of contamination by secondary transfer of GSR occurring during the transportation of a person under custody in a police vehicle should be evaluated. In order to investigate police vehicles as a source for secondary transfer of GSR particles, a total of 51 samples were collected from the rear seats of random police vehicles and used to transport arrested individuals. Results indicated that the type of upholstery of the seats plays a main role in determining the potential for secondary GSR contamination. The potential chance of coming into contact with GSR particles in police vehicles is low. GSR contamination from police vehicles is, maybe, not of a major concern but should be taken into consideration mainly when very few characteristic GSR particles are found on an analyzed sample.

Sensing of Gunshot Residue components from real sample using Fluorescence Resonance Energy Transfer.

The present work represents a Fluorescence Resonance Energy Transfer (FRET) based sensing method for detecting Gunshot Residue (GSR) components. Two laser dyes Acf and RhB have been used as donor and acceptor respectively in the FRET pair. The real sample was collected after test firing in a forensic science laboratory. On the other hand, a standard GSR solution has been prepared in the laboratory. For the preparation of standard GSR solutions, we used the water solutions of the salts BaCl2, SbCl3, and Pb(NO3)2. The FRET efficiency was measured between Acf and RhB to sense the presence of GSR components (Pb+2, Ba+2, and Sb+3) in both real sample and standard solution by mixing the salts in aqueous solution. It has been observed that the FRET efficiency systematically decreases in the presence of GSR components. To amplify the FRET efficiency of the dye pair, inorganic clay dispersion (laponite) was used. The enhancement in FRET efficiency represents a better sensitivity of the proposed sensor. The current sensor is useful for the quantification of concentrations of the GSR components in a real sample.