Discharge Residues from Cartridge-operated Industrial Tools

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.

Oral fluid as a new investigative matrix for the determination of organic gunshot residue exposure

In recent years, increased use of ammunition without lead and heavy metals was observed, leading to a growing interest in the detection of organic gunshot residues (OGSR) as evidence of firearms related crimes. The wide range of compounds belonging to the OGSR class hinders their mass spectrometric detection as different ionization techniques may be needed to obtain good results for all compounds. The purpose of this work was the development of a reliable analytical method by means of UHPLC-HRMS for the determination in oral fluid (OF) of the most common explosives and the most used stabilizers, arising from fire discharge and post-deflagration residues. For this purpose, SPE was used for OF clean-up before UHPLC-HRMS analysis. All target analytes were chromatographically separated by means of a Polar-C18 column. A chlorinated compound was added to the mobile phases in order to promote the formation of chloride adduct ions in the electrospray ion source operating in polarity switching to allow the best conditions for each analyte. The detection was conducted by means of a high-resolution mass spectrometer equipped with Orbitrap technology working in data dependent acquisition mode, in order to detect both the precursor ions and/or the most intense fragments for stabilizers. To verify its potential, the method was tested on real samples: a shooting session was performed in an open shooting range; the shooters fired from 2 to 20 rounds with a 9x21 caliber, thereafter OF was sampled. Samples were analyzed confirming that explosives may be detected in OF; the use of this matrix may be of great interest for investigative purposes as it is less affected by secondary transfer when compared to other commonly sampled matrices. The developed method could be a useful tool for law enforcement authorities for the detection of explosives in forensic potential scenarios, including biological matrices.

Rapid analysis of gunshot residues with single-particle inductively coupled plasma time-of-flight mass spectrometry

Gunshot residues (GSRs) from different types of ammunition have been characterized using a new method based on single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOF-MS). This method can analyze thousands of particles per minute enabling rapid sample screening for GSR detection with minimal sample preparation. GSR particles are multi-elemental nanoparticles that are mainly defined by the elements lead, barium, and antimony. Sp-ICP-TOF-MS was also used to identify other elements contained in GSR particles while standard particle classification protocols do not consider the complexities of GSR compositions and can therefore miss out on valuable information. The proposed method can be used to support existing GSR detection methods, especially when lead-free, antimony-free, or tagged ammunition has been used; it also provides a possibility for multi-elemental fingerprinting of GSR particles.

On the questioned presence of fluorine in inorganic gunshot residue. Case work experience and experimental evidences

According to the active ASTM E1588-20 Standard Practice for Gunshot Residue (GSR) Analysis, particles from lead-based primers classified as "characteristic of GSR" will have the chemical composition lead/antimony/barium. Further elements allowed to be incorporated into GSR are explicitly listed in the ASTM guideline. Fluorine is not considered a possible additional element as no common sources of F in shooting related activities have ever been documented. Moreover, presence of fluorine was demonstrated in GSR-similar particles produced by airbag deployments and the possibility to use F as a chemical marker to exclude any discharging of a firearm was consequently suggested. In authors' case work experience, fluorine containing particles were found on stubs collected from victims' clothes, discharged firearms and shooters' hands. Adopting a "case by case" approach, a firearm-related fluorine origin was then sought. Fluorine-based protective lubricants, used both for guns and ammunition components, were experimentally confirmed as a possible source of F in GSR.

Examination of gunshot residue arising from shotgun cartridges containing steel, bismuth or tungsten pellets

In Australia, shotguns feature in criminal activity and suicide shootings relatively frequently. However, compared to studies dealing with GSR originating from rifled firearms, those dealing with residues originating from shotguns are rare. The purpose of the research described in this article was to specifically characterize particle populations ejected from shotguns, and especially populations produced when ammunition containing steel shot was used, as it was expected that the high levels of iron likely to be produced during discharge may complicate GSR evidence evaluation. The expected high numbers of iron particles in GSR ejected from the muzzle of a shotgun during discharge of cartridges loaded with steel shot were not detected. The inevitable conclusion of that finding - that metal from the shot does not contribute to GSR ejected from the muzzle of a shotgun - was confirmed when practically no particles containing zinc were detected when cartridges loaded with zinc plated shot were fired. It is suggested that the shot-cup in the ammunition was very effective at preventing the formation of GSR particles from the shot. In contrast to those findings, high numbers of iron particles were detected in GSR ejected from the breech of a shotgun when ammunition loaded with steel shot was fired. However, when ammunition loaded with bismuth or tungsten shot was fired, the levels of tungsten and bismuth particles ejected were very low but high numbers of iron particles were still detected. It is suggested that the firing mechanism in the gun itself, rather than the ammunition used, is responsible for the abundance of iron detected in GSR ejected from the breech. Despite the presence of iron in shotgun GSR, typical primer-derived residues (containing any or all of the elements lead, barium and antimony) were detected in residues ejected from the muzzle and the breech therefore evidence evaluation is relatively straightforward.

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.

Detection of gunshot residues using mass spectrometry

In recent years, forensic scientists have become increasingly interested in the detection and interpretation of organic gunshot residues (OGSR) due to the increasing use of lead- and heavy metal-free ammunition. This has also been prompted by the identification of gunshot residue- (GSR-) like particles in environmental and occupational samples. Various techniques have been investigated for their ability to detect OGSR. Mass spectrometry (MS) coupled to a chromatographic system is a powerful tool due to its high selectivity and sensitivity. Further, modern MS instruments can detect and identify a number of explosives and additives which may require different ionization techniques. Finally, MS has been applied to the analysis of both OGSR and inorganic gunshot residue (IGSR), although the "gold standard" for analysis is scanning electron microscopy with energy dispersive X-ray microscopy (SEM-EDX). This review presents an overview of the technical attributes of currently available MS and ionization techniques and their reported applications to GSR analysis.

An assessment of firework particle persistence on the hands and related police force practices in relation to GSR evidence

In a previous study by Grima et al. Sci. Justice 52 (1) (2012) 49, it was shown that background particles can aid in the exclusion of firework particles which are indistinguishable from GSR. Issues relating to the persistence of such particle populations were presented. The scope of this project was to examine persistence on the hands in the context of possible post-display scene contamination and how this can affect GSR evidence, especially in light of possible GSR/firework mixtures. Persistence was investigated by recovering firework residues eight hours post-display following contact of the hands with bedding. In addition, particle profiling was carried out using SEM-EDX. Firework particle populations exhibited strong persistence in all displays, with not less than 667 particles persisting in each scenario. This factor challenges GSR evidence, especially if personnel stationed at display sites enter scenes of crime or come into contact with suspects after a display. A survey of UK police force practices following firework displays showed that authorities are not aware of the impact particle transfer may have on GSR evidence. Recommendations for the implementation of basic hygiene practices for particle transfer control have also been made.

Determining the lifetime of detectable amounts of gunshot residue on the hands of a shooter using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used to determine the period of time that a shooter will test positive for gunshot residue (GSR) after firing a revolver. Multiple rounds of primer were fired and samples collected at multiple hour intervals using an adhesive tape pressed against the skin. Samples were analyzed directly using a commercially available laser-induced breakdown spectrometer where barium emission (originating from barium nitrate in the primer) was observed. Population statistics were used to compare suspected GSR to a library of blank samples from which a threshold value was established. Statistically significant results, positive for GSR, are obtained 5.27 days after a firearm discharge using these techniques.

A proposal for statistical evaluation of the detection of gunshot residues on a suspect

The possibility of accidental contamination of a suspect by gunshot residues (GSRs) is considered. If two hypotheses are taken into account ("the suspect has shot a firearm" and "the suspect has not shot a firearm"), the likelihood ratio of the conditional probabilities of finding a number n of GSRs is defined. Choosing two Poisson distributions, the parameter lambda of the first one coincides with the mean number of GSRs that can be found on a firearm shooter, while the parameter mu of the second one is the mean number of GSRs that can be found on a nonshooter. In this scenario, the likelihood ratio of the conditional probabilities of finding a number n of GSRs in the two hypotheses can be easily calculated. The evaluation of the two parameters lambda and mu and of the goodness of the two probability distributions is performed by using different sets of data: "exclusive" lead-antimony-barium GSRs have been detected in two populations of 31 and 28 police officers at diverse fixed times since firearm practice, and in a population of 81 police officers who stated that they had not handled firearms for almost 1 month. The results show that the Poisson distributions well fit the data for both shooters and nonshooters, and that the probability of detection of two or more GSRs is normally greater if the suspect has shot firearms.

Application of lead isotope analysis in shooting incident investigations

A study was conducted to examine the potential of the considerable variability of the lead isotope compositions in bullets (projectiles) and primers in shooting incident investigations. Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP/MS) was used to analyze lead isotopic compositions in projectiles, cartridge cases, firearms discharge residues (FDR) in barrels of firearms and in the gunshot entries. .22 caliber plain lead and plated ammunition and 9 mm Luger full metal jacket (FMJ) ammunition were employed in shooting experiments using semiautomatic pistols. Cotton cloth served as the target material and two firing distances were tested; 1 cm (near contact) and 2 m distances. It was observed that various mechanical or chemical means of cleaning do not completely remove lead deposits ("lead memory") from barrels of firearms. Nonetheless, it was shown that analysis of lead isotopic composition may provide valuable evidence in investigating specific scenarios of shooting incidents. For instance in a shoot-out where several firearms and ammunition brands are involved, it may be feasible to point out which ammunition and/or firearm caused a particular gunshot entry if the ammunition brands involved (bullets and primers) differ considerably in their lead isotopic composition.

X-ray mapping technique: a preliminary study in discriminating gunshot residue particles from aggregates of environmental occupational origin

The possibility of detection of lead-antimony-barium aggregates from non-firearm sources is confirmed according to the tests performed on brake pads, and firework and automobile workers. Moreover, information on particles taken from cartridge cases shows the relative feeble importance of the morphology in distinguishing gunshot residues (GSRs). Furthermore, also the presence in the spectrum of other elements (e.g., iron) is not so conclusive. In this panorama, the possibility of discriminating gunshot residue particles from other non-firearm lead-antimony-barium aggregates is investigated: the proposed method is based on X-ray mapping technique--currently applied used in Reparto Carabinieri Investigazioni Scientifiche in Rome, the forensic service of Italian Carabinieri--according to which the spatial distribution of the emission energy of each element of the sample is pictured. Gunshot residues present the same lead-antimony-barium distribution (or at least the same antimony-barium distribution with lead nodules), as some other environmental occupational aggregates do not (different plaques of lead, antimony, and barium). So, X-ray mapping technique can offer a new fundamental evaluation parameter in analysis of gunshot residues with scanning electron microscopy/energy-dispersive (SEM/EDS) spectrometry, and new standards could be considered.

Laser-induced breakdown spectroscopy for the detection of gunshot residues on the hands of a shooter

Laser-induced breakdown spectroscopy (LIBS) has been used to determine whether the hands of a suspected gun user contain traces of gunshot residue. Samples are obtained by pressing adhesive tape against the skin of the suspect and analyzing the tape directly. When the suspect has fired multiple shots, or if the gun has not been cleaned, the gunshot residue provides a spectral signature that is readily apparent, but a person who has fired a single shot from a clean gun is not so easy to identify. The error rates associated with the LIBS identification of a subject who fired one shot from a clean gun have been evaluated by Monte Carlo simulation techniques, and criteria are proposed for defining a positive or a negative test result.

Hair combing to collect organic gunshot residues (OGSR)

A protocol is presented for the collection and analysis of gunshot residues (GSR) from hair. A fine-toothed comb is used for collection of the residues. A small zip-closure bag serves as a container for both sample storage and extraction of the characteristic organic powder additives. The success of this residue recovery approach was tested on simulated shooters and victims using mannequin-supported human wig hair as well as on human shooters. Residues were collected from four weapons: a revolver and semi-automatic pistol, rifle and shotgun. One characteristic additive, nitroglycerin, was detected by capillary electrophoresis (CE) in the majority of the collection experiments.

Identification of gunshot residue: a critical review

A review of the scientific papers published on inorganic gunshot residue (GSR) analysis permits to study how the particle analysis has shown its capability in detection and identification of gunshot residue. The scanning electron microscope can be the most powerful tool for forensic scientists to determine the proximity to a discharging firearm and/or the contact with a surface exposed to GSR. Particle analysis can identify individual gunshot residue particles through both morphological and elemental characteristics. When particles are detected on the collected sample, the analytical results can be interpreted following rules of a formal general interpretative system, to determine whether they come from the explosion of a primer or from other possible sources. The particles on the sample are compared with an abstract idea of "unique" GSR particle produced by the sole source of the explosion of a primer. "Uniqueness" is not the only problem related to GSR detection and identification for a forensic scientist. With "not-unique" particles interpretation of results is extremely important. The evidential strength of "not-unique" particles can increase with a more fruitful interpretative framework based on Bayes rule. For the assessment of the value of a GSR in linking a suspect and a crime, it is important to compare two hypothesis: the first can be that of the evidence if the suspect has been shooting in a specific situation, the second that of the evidence if the suspect was not involved in this shooting. This case specific or case-by-case approach is closer to what the court is interested in. The authors consider that a "case-by-case" approach should be followed whenever possible. Research of models and data such as those developed in other trace evidence material (fibres, glass, etc.) using a Bayesian approach is suggested in the interpretation of GSR.

Cartridge discharge residue contamination--the search for the source

The detection of cartridge discharge residue (CDR) particles on some control samples in a firearms case started an extensive search to discover their origin. Investigation of potential sources of the contamination showed that it was airborne but random in nature, and it is recommended that frequent examination of air control samples should be made in contamination-sensitive areas.