Tandem detection of organic and inorganic gunshot residues using LC-MS and SEM-EDS.

Gunshot residue (GSR) is a valuable form of forensic trace evidence in the investigation of firearms crime. The current gold-standard approach does not include the analysis of organic components of the residues, which may be a deficiency, particularly in cases where there is little to no inorganic gunshot residue (IGSR) present or its attribution to a firearm source is ambiguous. A solvent extraction method was used for the extraction of organic GSR (OGSR) from the most common sampling device used to collect IGSR (i.e., SEM stubs with double-sided carbon adhesive tape). It was found that extraction did not significantly disturb inorganic GSR present on stubs, which raises the possibility that a valuable, comprehensive tandem analysis of both organic and inorganic GSR may be implemented using a single and commonly used residue collection device. The organic extract was analysed using Ultra High Performance Liquid Chromatography coupled to an Ion Trap Mass Spectrometer using Electrospray Ionisation (UHPLC-ESI-MS/MS), with preliminary results indicating that organic components can be extracted and detected at levels appropriate to casework GSR analysis. Testing of traces collected from the hands of recent shooters showed detection of stabiliser compounds typical of OGSR, which were confirmed to be present in the test ammunition's propellant. Total analysis time is approximately 30min per specimen, including preparation, instrumental analysis and data review. As the first step in the examination of GSR stubs in relation to a shooting case, extraction of organics and analysing them for the presence of OGSR may bring two operational benefits. First, that approach may be a useful way to determine which stubs warrant priority examination for IGSR, and second, it offers the possibility of providing relatively rapid case information to investigators.

Evaluation of the sub-surface morphology and composition of gunshot residue using focussed ion beam analysis.

Recent work in the forensic analysis of Gunshot residues (GSR) has suggested that the sub-surface or internal composition and morphology of these residues be explored. A particular area of interest is in heavy metal free, or non-toxic ammunition, which are becoming more frequently encountered in the marketplace. As the formulation of the primer compound changes the conditions of the firearm discharge, there is the possibility that different primer formulations may result in the formation of different GSR particles with distinct internal morphologies and compositions. To that end, the internal morphology and composition of GSR particles may provide additional information that could be useful in the investigation of firearms crime. This research investigated the internal morphology of GSR originating from a variety of different ammunition products. Both traditional three-component primed ammunition, and a selection of heavy metal free and non-toxic alternatives were considered. Particles were identified using SEM-EDS, before being cross-sectioned using a focussed ion beam (FIB) instrument. The FIB-sectioned particles were then re-acquired and mapped using SEM-EDS, to assess both internal morphology and composition. Particles observed in this study presented distinct morphological and compositional features at the sub-particle level that may provide an indication of the primer formulation from which they originated. That said, further investigation of a variety of samples should be undertaken to verify the consistency of these features, or any deviations that may be observed based on primer type. However, these results indicate that there may be promise in obtaining additional detail from sub-particle morphology and composition.

Methods for analysis of glass in glass-containing gunshot residue (gGSR) particles.

When lead, barium and antimony, or lead, barium, calcium, silicon and tin are found together in particles associated with a shooting investigation they are considered characteristic of gunshot residue (GSR). Antimony and tin are often absent from the primer of many low calibre rimfire ammunitions, which are the type most commonly used in Australia. Therefore, the likelihood of characteristic particles forming during the firing process of such rimfire ammunition is significantly less than the likelihood of these particles arising from higher calibre ammunition. The majority of rimfire ammunition examined in this research contains ground glass in the primer, which functions as a frictionator. These ammunitions produce a small number of gunshot residue particles containing glass coated with other primer components, which we refer to as glass-containing GSR (gGSR). If these particles are observed in an investigation, they have the potential to add a new dimension to gunshot residue analysis because they are not common in the environment. Furthermore, the composition of glass frictionator is stable during firing, which raises the possibility that chemical testing of the glass in gGSR may be used to identify the ammunition from which the residue was derived or to link deposits of GSR. This paper examines the application of scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), focussed ion beam (FIB) techniques and time of flight-secondary ion mass spectrometry (ToF-SIMS) to the semi-quantitative analysis and comparisons of gGSR and frictionator extracted from unfired cartridges. SEM-EDS is effective for comparing gGSR with unfired frictionator, but the use of FIB to expose clean glass from the centre of gGSR followed by ToF-SIMS, or ToF-SIMS using ion sputtering to expose clean glass, offers more power for comparisons due to their capability for higher discrimination between frictionators from different sources.

Glass-containing gunshot residues and particles of industrial and occupational origins: Considerations for evaluating GSR traces.

In an ideal case, the value of traces would be determined numerically and presented through the use of likelihood ratios or verbal-equivalent scales. A problem in the evaluation of gunshot residue (GSR) evidence using these models is that in many shooting scenarios insufficient data exist to support a quantitative model of interpretation. The complex relationship that exists between ammunition composition and post-firing residues makes quantitative interpretation more difficult for GSR than for other traces such as glass. When evaluating the significance of traces in a quantitative model, the value of a trace is reduced as the number of random sources that could produce the trace increases. Previously published works have suggested that glass-containing GSR (gGSR), which is glass encrusted with lead (Pb) and barium (Ba) residues, are a new type of GSR not already classified under ASTM E1588 - 17. If random sources of particles resembling gGSR are rare, then gGSR may be valuable evidentiary traces. In order to potentially incorporate these particles into a future model, the general background prevalence of gGSR and specific sources capable of producing similar particles must be understood. Therefore, particles from fireworks, matches, and cartridge actuated nail guns were assessed on an individual basis and at a population level. These sources, known to produce particles resembling GSR, were assessed using backscattered electron - scanning electron microscopy - energy dispersive X-ray spectroscopy analysis (BSE-SEM-EDS) for the presence of glass-containing particles that resemble gGSR. In the experiments described in this article the nail gun produced particles compositionally indistinguishable from gGSR, due to the primer in the brand of nail gun cartridges used containing glass as the frictionator in addition to Pb and Ba compounds. In this study, no particles were located from fireworks or matches that were indistinguishable from gGSR, nor was any evidence observed or found in the literature that would suggest that such particles could be formed.

Analysis of elemental and isotopic variation in glass frictionators from 0.22 rimfire primers.

The majority of 0.22 calibre rimfire ammunition available in Australia, and overseas, tends to use glass powder rather than antimony sulfide frictionator in the primer. This glass can be the nucleus of a GSR particle, with other primer components condensing around and onto the glass structure. As the composition of glass frictionator remains largely unaltered during ammunition discharge [1] there is the possibility that frictionator composition could be used in GSR examinations to either correlate or discriminate between samples, thereby providing valuable information to an investigation. In this study, the composition of glass frictionator from a wide variety of ammunition was analysed by time-of-flight - secondary ion mass spectrometry (ToF-SIMS), sensitive high-resolution ion microprobe (SHRIMP) and scanning electron microscopy - energy dispersive X-ray spectrometry (SEM-EDS). Refractive index (RI) was measured using glass refractive index measurement (GRIM). Across the population of ammunition studied, it was found that the elemental and isotopic composition of frictionator varied. ToF-SIMS was able to discriminate 94.1% of brands in a pairwise comparison and SEM-EDS achieved a pairwise discrimination power of 79.4%. If SHRIMP was combined with the other two techniques, 95.6% of brands could be discriminated. Refractive index measurements supported the elemental data showing that there appeared, in most cases, to be only one population of glass within a cartridge. The results suggest that there is scope for frictionator analysis to contribute valuable, new capability to forensic GSR examinations.

Gunshot residue and brakepads: Compositional and morphological considerations for forensic casework.

Previous research has raised the possibility that automotive brake pads can produce particles that are both compositionally and morphologically similar to gunshot residue (GSR). These studies, published in the early 2000s, coincided with the reduction or removal of unnecessary sources of lead from the automotive industry. The question therefore arises whether modern brake pads might still be a relevant source of 'GSR-like' particles. In the present study, a total of 75 brake pads taken from a range of cars currently on the road in Adelaide, South Australia, were collected from service centres. These pads were screened by XRF, and 12 were selected as representatives of the types of pads available on the market. Some pads generated XRF results for elements particularly relevant to GSR analysis. Signals for barium and antimony were commonly observed, with some pads showing results possibly attributable to lead. The surfaces of these 12 pads were directly sampled using aluminium stubs equipped with carbon-filled adhesive tape. Following this, they were screened using SEM-EDS and an automated GSR particle search in order to detect particles containing lead, barium or antimony. No particles containing all of these elements were found, although a large number of particles containing both barium and antimony were located. Other particulate samples were collected using stubs from persons or objects associated with brakes in order to examine whether particles similar to GSR might be present on them. No three-component particles were detected in samples collected from the wheel rims or the hands of those exposed to automobiles. From this study of common, contemporary cars, brake pads and brake pad technicians, it was determined that the possibility of obtaining three-component 'GSR-like' particles from brake pads appears to be much lower now than when this issue was first raised in the early 2000s. While some brake pads do produce particles containing barium and antimony, they are often angular particles that contain sulphur. Furthermore, these 'GSR-like' particles are commonly found together with an abundance of particles containing iron. The particle evidence evaluated in total allows clear differentiation between residues originating from brakes and residues originating from firearms.

Glass fragments from portable electronic devices: Implications for forensic examinations.

Personal electronic devices (PEDs) are now widespread in the community. Many such devices have glass display screens that, despite being a relatively strong and specialised material, are vulnerable to breakage. Unlike other glass objects that are usually thrown away when they break, PEDs can still function with a broken or cracked screen and it is not uncommon for their owners to keep using them in this condition. Broken PED screens, therefore, might represent a new and significant source of glass fragments that are present on the clothing and belongings of the general public and individuals suspected of offences involving the breaking of glass. The forensic implications of this new source of glass fragments in the community were investigated. PED glass is easily recognised using scanning electron microscopy-energy dispersive X-ray analysis and refractive index measurement and is easily distinguished from domestic and automotive soda-lime glass using these methods; as a consequence there should be no confusion of soda-lime glass fragments and PED glass fragments in forensic glass casework. In cases where the objective is to compare recovered glass fragments to a putative PED source, comparison using refractive index measurement and elemental analysis achieves good discrimination between sources.