Interpol Review of Gunshot Residue 2019 to 2021

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.

The development of screen-printed electrodes modified with gold and copper nanostructures for analysis of gunshot residue and low explosives

Due to their portability, sensitivity, and ease of use, electrochemical sensors have recently become a popular method for rapid, on-site analysis. This study presents a proof of principle for the application of modified screen-printed carbon electrodes (SPCEs) for the detection of signature metals (Pb, Sb, and Zn) commonly found in gunshot residue (GSR), as well as for the detection of nitrate/nitrite in organic GSR and low explosives. To achieve these two aims, we have examined various electrode surface modifications. For metal detection, SPCEs were modified by electrodeposition of gold to improve sensitivity. GSR samples taken from two types of cartridge cases and shooting-related surfaces were analyzed using the Au-modified SPCEs. For nitrate/nitrite analysis, further electrode surface modifications were carried out by depositing Cu(II) onto the Au-SPCEs to enhance signal through catalytic activity of the copper surfaces. Both unburned and burned forms of black powder samples, as well as burned smokeless powder, were then analyzed using the Cu/Au-SPCEs. In conclusion, due to their low cost and portability, these sensors should prove useful for rapid forensic examination.

Police vehicle contamination by inorganic gunshot residue (iGSR) in Zagreb County Police Administration (Croatia): Analysis of characteristic and indicative particles across different vehicle parts and contributory risk factors

Inorganic gunshot residue (iGSR) analysis, crucial for linking suspects to firearm use, faces challenges from potential environmental contamination, notably in police vehicles. The present study aimed to explore the level of iGSR contamination in police vehicles from the Zagreb County Police Administration (Croatia), considering particle types and their position in vehicles, and to identify associated risk factors. From December 2021 to April 2022, 65 of 86 police vehicles (margin of error: ±6% at a 95% confidence level) were sampled with GSR stubs on the drivers' seats, back seats, and backrests and analyzed using scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDX). Characteristic particles were found in 63.1% of vehicles, 33.8% on the driver's seat, and 24.6% on the back seat/backrest. Indicative particles were found in 70.77% of vehicles, with a fairly even distribution. McNemar's chi-square analysis showed no significant disparities in positive sample ratios across vehicle parts or particle types (p > 0.05). In total, 228 characteristic and 166 indicative GSR particles were identified, with no notable correlation among them (p = 0.346). Logistic regression analysis identified the transportation of individuals involved in firearms incidents as a statistically significant factor influencing the presence of characteristic particles (p = 0.030). The findings suggest a considerable prevalence of iGSR in the analyzed Police Administration unit, highlighting the need for careful contamination management in police operations to preserve evidence integrity, particularly in cases when individuals who used firearms had been transported in the vehicle.

Identifying Sample Provenance From SEM/EDS Automated Particle Analysis via Few-Shot Learning Coupled With Similarity Graph Clustering

Automated particle analysis (APA) provides a vast amount of compositional data via energy-dispersive X-ray spectroscopy along with size and shape data via scanning electron microscopy for individual particles in a sample. In many instances, APA data are leveraged to support identification of the source of a sample based on the detection of particles of a specific composition. Often, the particles that provide context make up a minuscule portion of the sample. Additionally, the interpretation of complex samples can be difficult due to the diversity of compositions both in the mixture and within a particle. In this work, we demonstrate a method to compute and cluster similarity graphs that describe inter-particle relationships within a sample using a multi-modal few-shot learning neural network. As a proof-of-concept, we show that samples known to have been exposed to gunshot residue can be distinguished from samples occasionally mistaken for gunshot residue. Our workflow builds upon standard APA techniques and data processing methods to unveil additional information in a readily interpretable and quantitatively comparable format.

Beyond the shot: Exploring secondary transfer of gunshot residue on common surfaces and the impact of hand cleaning methods

Understanding the presence, transfer dynamics and depletion of gunshot residues (GSR) on various surfaces is crucial for preserving evidence, reconstructing shooting incidents, and linking suspects to crime scenes. This study aims to explore the transfer and loss of GSR on commonly encountered surfaces such as ceramic, glass, metal, paper, and plastic, as well as the influence of different common hand cleaning methods on secondary transfer. Using scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) and automated detection software, we quantified highly indicative three-component characteristic particles (lead, barium, and antimony) on cups made from ceramic, glass, metal, paper, and plastic. Furthermore, we evaluated the amount of secondary transferred particles on these surfaces following various post-discharge hand cleaning methods: washing with water and soap, washing with only water, wiping with wet wipes, or using paper towels. The results demonstrate that counts of secondarily transferred GSR particles vary significantly among surfaces. Specifically, the transferred GSR count was highest on paper, followed by plastic, ceramic, metal, and glass respectively. Post-discharge hand cleaning methods, including washing with water and soap, washing with only water, cleaning with wet wipes, or with paper towel, resulted in substantial loss of GSR count on transferred surfaces. Among these methods, washing with water and soap showed the highest depletion. The empirical evidence provided by our results underscores the importance of considering surface properties, post-shooting activities, and the methods of sample collection and analysis when interpreting transferred GSR analysis. Despite challenges, these insights enhance our ability to link suspects to shooting crimes through careful consideration of the entire context.

Quantitative PCR overestimation of DNA in samples contaminated with tin

Metals can pose challenges while conducting forensic DNA analysis. The presence of metal ions in evidence-related DNA extracts can degrade DNA or inhibit PCR as applied to DNA quantification (real-time PCR or qPCR) and/or STR amplification, leading to low success in STR profiling. Different metal ions were spiked into 0.2 and 0.5 ng of human genomic DNA in an "inhibition study" and the impact was evaluated by qPCR using the Quantifiler™ Trio DNA Quantification Kit (Thermo Fisher Scientific) and an in-house SYBR Green assay. This study reports on a contradictory finding specific to tin (Sn) ions, which caused at least a 38,000-fold overestimation of DNA concentration when utilizing Quantifiler Trio. This was explained by the raw and multicomponent spectral plots, which indicated that Sn suppresses the Quantifiler Trio passive reference dye (Mustang Purple™, MP) at ion concentrations above 0.1 mM. This effect was not observed when DNA was quantified using SYBR Green with ROX™ as the passive reference, nor when DNA was extracted and purified prior to Quantifiler Trio. The results show that metal contaminants can interfere with qPCR-based DNA quantification in unexpected ways and may be assay dependent. The results also highlight the importance of qPCR as a quality check to determine steps for sample cleanup prior to STR amplification that may be similarly impacted by metal ions. Forensic workflows should recognize the risk of inaccurate DNA quantification of samples that are collected from substrates containing tin.