A study of transfer and prevalence of organic gunshot residues

Uncovering gunshot residue flow and deposition mechanisms using novel visualization methods, real-time atmospheric particle sampling, and spectrochemical techniques

Gunshot residue (GSR) consists of inorganic and organic components released during firearm discharge. Understanding the generation, transport, and settlement of these residues is essential to assess exposure risks and answer questions of forensic interest. Since GSR is prone to depositing in the vicinity of a firing event, its presence on a person of interest is meaningful to evaluate hypotheses about who discharged a firearm or if GSR was acquired by alternative means such as indirect transfer, being a bystander, or passing through the area shortly thereafter. However, the complexity of GSR production and variable dispersion makes its interpretation challenging. This study employs a novel multi-sensor approach to enhance the current understanding of GSR deposition, transference, and persistence. First, a particle counting/sizing system and inexpensive custom-made atmospheric samplers measure the population of airborne particles before, during, and after the firearm discharge. Second, high-speed videography and laser sheet scattering reveals visual and qualitative information about the flow of GSR under various experimental conditions. Finally, SEM-EDS and LC-MS/MS permit the confirmation of the elemental and chemical makeup of residues. This study estimates (a) how IGSR/OGSR are produced during a firing event using various firearms and ammunition, (b) how long it takes to settle on surfaces located at various distances from the firing location, and (c) direct and indirect deposition in indoor, semi-enclosed, and outdoor environments. The combination of these analytical tools provides breakthrough knowledge in forensics and other disciplines where airborne exposure is central, such as environmental sampling and indoor air quality.

Exploring gunshot residue detection in fingerprints by functionalized particle-coupled matrix-assisted laser desorption/ionization mass spectrometry

In firearm forensic investigations, detecting gunshot residue (GSR) is crucial for linking firearms to suspects and determining firing distance for forensic reconstruction. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS) is emerging as a versatile and promising technological platform for fingerprint analysis. The capability of functionalized particles as an advanced dusting powder for visualizing latent fingerprints is widely recognized. This study aims to investigate the feasibility of employing functionalized magnetic fingerprint dusting powders for distinguishing regular and GSR fingerprints using MALDI-ToF-MS, thereby enhancing forensic evidentiary support. In this study, silica and carbon coated magnetic iron oxide particles were surface functionalized with phenyltriethoxy orthosilicate (PTEOS) or 3-aminopropyl triethoxysilane (APTES) to create hydrophobic and hydrophilic particles, respectively. Donor shooters' fingerprints, both GSR-containing and regular, were analyzed using these functionalized particles coupled with MALDI-ToF-MS. The results demonstrated effective fingerprint visualization and conclusive discrimination between GSR-containing and regular fingerprints through orthogonal partial least squares discriminant analysis. This technique provides enhanced sensitivity, speed, and adaptability compared to conventional methods, making it a promising choice for initial detection of GSR in latent fingerprints. Moreover, when subjected to thorough analysis using advanced instruments, it has the potential to significantly strengthen the probative value of fingerprint evidence in forensic investigations.

Organic and inorganic gunshot residues on the hands, forearms, face, and nostrils of shooters 30 min after a discharge

During the investigation of firearm-related incidents, gunshot residues (GSR) can be collected on the scene and individuals (e.g., shooters or bystanders). Their analysis can give valuable information for the reconstruction of the events. Since GSR collection on persons of interest generally occurs a few minutes to hours after discharge, knowledge is needed to understand how organic (O), and inorganic (I) residues are transferred and persist. In this research, the quantities of OGSR and IGSR were assessed on the right and left hands, forearms, face, and nostrils of four shooters. Specimens were collected immediately before the discharge (shooter's blank specimens) and shortly after (30 min) using carbon adhesive stubs. Organic compounds were first extracted from the collection device and analysed using ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Subsequently, IGSR particles were detected on the same stub using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS). Shooter's blank specimen analysis revealed background contamination of both O and IGSR in the shooter's environment, predominantly attributed to the presence of an indoor shooting range. However, the background quantities generally remained below the associated 30-minute specimen. Thirty minutes after a discharge, higher quantities were generally detected on the shooter's right and left hands than on other collection regions for both GSR types. Forearms and face emerged as interesting collection alternatives, especially in cases where a person of interest may have washed their hands in the interval between the discharge and collection. In contrast, very low amounts of GSR were detected in the nostrils. Furthermore, the results indicated that OGSR and IGSR have different transfer and persistence mechanisms.

[Current approaches for sampling to study the traces of gunshot residue]

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.

LC-MS/MS monitoring for explosives residues and OGSR with diverse ionization temperatures in soil & hands: 30 minutes for extraction + elution

A fast LC-APCI-MS/MS screening/confirmation method was developed and validated for trace analyses of 18 analytes which are explosives and organic gun shot residues including the challenging ones with diverse ionization conditions, in soil and on hands. (+) and (−) ionization modes were used after a single-step, low-volume solvent extraction procedure developed using methanol. Tape-lifting, stub, alcohol wipes, cotton bud were compared for collecting the residues from hands of a shooter. Tape-lifting and stub gave the highest recoveries and tape-lifting was chosen. Gradient elution system using ammonium chloride:methanol was developed. Whole procedure lasted approximately 30 min, was validated in both matrices, applied to real samples as post-blast residues, smokeless powder and the hands of a shooter, after shooting. Most of the recoveries were >80% and since all the precisions were <15%, quantitation was possible for all. Limit of Detection (LOD) and Limit of Quantification (LOQ) values were: 0.2–54.1 and 0.3–190.0 ngg−1 in soil, and 0.2–132.3 and 1.1–355.0 ngg−1 in tape-lift.

Interpol review of gunshot residue 2016-2019

This review paper covers the forensic-relevant literature in gunshot residue analysis from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Armed with the Facts: A Method for the Analysis of Smokeless Powders by Ambient Mass Spectrometry

The work presented here follows several others in investigating what capabilities, if any, ambient mass spectrometry might have toward the analysis of compounds commonly associated with smokeless propellant powders. This family of instrumental techniques has attracted curiosity from the field of forensic science due to its desirable properties such as rapid collection of information-rich data, combined with minimal requirements for sample mass and preparation. Experiments were conducted with a "Direct Sample Analysis" ion source integrated with a time-of-flight mass spectrometer. The ionization behaviors of nitroglycerin, methyl and ethyl centralite, akardite, diphenylamine, nitrosodiphenylamine, and nitrated diphenylamine derivatives were investigated specifically, with accurate-mass data presented for each. Diphenylamine standards were used to demonstrate the performance of this instrument, which exhibited good response linearity across 1 order of magnitude and sub-nanogram detection limits. Thirty smokeless powder extracts, recovered from ammunition potentially in circulation within Australia, were analyzed to determine whether the technique is appropriate for rapid analysis of smokeless powder particles. Results demonstrated that the technique might be applied to compare individual particles with each other or to a database. Such a capability may be of value in the examination of explosive devices containing smokeless powder, postblast residues therefrom, or muzzle discharge from a close-range shooting. However, when efforts were made to detect residues from the hands of a volunteer shooter, only some returned positive results, and a high background signal from the sample collection stub indicates that detection using this instrument is thus far insufficiently reliable.

Chemical Classification of Explosives

This work comprehensively reviews some fundamental concepts about explosives and their two commonly used classifications based on either their velocity of detonation or their application. These classifications are highly useful in the military/legal field, but completely useless for the chemical determination of explosives. Because of this reason, a classification of explosives based on their chemical composition is comprehensively revised, discussed and updated. This classification seeks to merge those dispersed chemical classifications of explosives found in literature into a unique general classification, which might be useful for every researcher dealing with the analytical chemical identification of explosives. In the knowledge of the chemical composition of explosives, the most adequate analytical techniques to determine them are finally discussed.

Prevalence of organic gunshot residues in police vehicles

The present study investigated the organic gunshot residue (OGSR) background level of police vehicles in Switzerland. Specimens from 64 vehicles belonging to two regional police services were collected and analysed by LC-MS in positive mode. The driver's and back seats were sampled separately to monitor potential differences between locations and to assess the risks of a suspect being contaminated by OGSR during transportation to a police station. The results showed that most of the 64 vehicles were uncontaminated (44 driver's seats and 38 back seats respectively). Up to six of the seven targeted compounds were detected in a single sample, once on a driver's seat and twice on back seats. The contamination frequency generally decreased as the number of compounds detected together increased. The amounts detected were in the low ng range and less than amounts generally detected just after discharge on a shooter. Our data indicated that detecting a combination of four or more compounds on a police vehicle seat appears to be a relatively rare occurrence. The background contamination observed was most probably due to secondary transfer from police officers (e.g. through recent participation in a shooting session or firearm manipulation) or from firearms stored in the vehicles. The present results might be used as a recommendation to minimize contact of a suspect with contaminated surfaces if OGSR is implemented in routine work in parallel to IGSR analysis.