Secondary transfer of organic gunshot residues: Empirical data to assist the evaluation of three scenarios

The present study aimed at providing data to assess the secondary transfer of organic gunshot residues (OGSR). Three scenarios were evaluated in controlled conditions, namely displacing a firearm from point A to point B, a simple handshake and an arrest involving handcuffing on the ground. Specimens were collected from the firearm, the hands of the shooter and the non-shooter undergoing the secondary transfer in order to compare the amounts detected.Secondary transfer was observed for the three scenarios, but to a different extent. It was found that displacing a firearm resulted in secondary transfer in <50% of the experiments. The firearm also had an influence, as contrary to the pistol, no secondary OGSR were detected using the revolver. Shaking the hand of the shooter also transferred OGSR to the non-shooter's hand. In that case, the amount of OGSR was generally higher on the shooter than on the non-shooter. Finally, the largest secondary transfer was observed after the arrest with handcuffing with positive results in all cases using the pistol. In that scenario, the amounts on the shooter and the non-shooter were in the same range.This study highlights that the secondary transfer must be taken into account in the interpretation of OGSR. Indeed, an individual's hands might be contaminated by handling a firearm or having physical contact with a shooter.     

An investigation on the secondary transfer of organic gunshot residues

Gunshot residues (GSR) are an important forensic trace in firearm-related events. Currently, routine GSR analyses focus on the detection and characterisation of the inorganic components (IGSR). The increasing prevalence of heavy metal-free ammunition challenges these current protocols and there is an increasing interest in how the organic components of GSR (OGSR) can provide complementary information. Similar to the situation with IGSR, OGSR compounds originally deposited on the shooter during the firing process may further be transferred onto another individual or surface. Hence, the aim of this study was to provide additional information regarding the risk of a secondary transfer of OGSR. Two scenarios were investigated, the first one related to the arrest process and the possibilities of a secondary transfer arising between a shooter onto a non-shooter (e.g. between a police officer and a person of interest (POI)). The second scenario concerned the transfer of OGSR onto the non-shooter after handling a firearm for few minutes without discharging it. One calibre was chosen, the .40 S&W calibre, used by several Australian State police forces. A secondary transfer was observed in all cases for the two scenarios investigated, for three compounds of interest: ethylcentralite (EC), diphenylamine (DPA), N-nitrosodiphenylamine (N-nDPA). The firearm handling scenario resulted in a larger secondary transfer to that of the arrest scenario. Overall, the amounts of OGSR detected on the non-shooter were generally lower than that detected on the shooter and controls after the arrest scenario. The results of this study provide complementary knowledge about OGSR, which can be further used to improve the current practice and the interpretation of OGSR evidence. In particular, it highlights that the secondary transfer proposition must be considered during the interpretation of forensic findings, especially when small amounts of OGSR target compounds are detected.     

Comparison of three collection methods for the sodium rhodizonate detection of gunshot residues on hands

The aim of this study was to compare three gunshot residue (GSR) collection methods used in conjunction with chemographic detection applied by different regional Swiss police services. The specimens were collected from the hands of a shooter with either filter paper (Filter method) or adhesive foil. The adhesive foil was then either applied against photographic paper during visualisation (AF Photo method) or coated with a layer of polyvinyl alcohol (AF PVAL method). The experiments involved two conditions of the examined hands, i.e. dry and humidified. The residues were revealed using the sodium rhodizonate test (SRT). Preliminary tests assessing the possibility of conducting a confirmatory Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis after the chemographic test were performed on a number of specimens by cutting positive spots and mounting them on stubs. Obtained results were compared in terms of effectiveness - number of positive spots, time requirements, quality of subsequent SEM-EDX analysis, ease of use and cost.The Filter method generally yielded a high-quality detection with both dry and humidified hands, as well as a simple, quick and efficient confirmation by SEM/EDX. The AF Photo performed well on dry hands, but not on humidified hands. The AF PVAL method performance was lower compared to the other methods in both examined conditions of the hands. The SEM/EDX analysis showed that the Filter and AF PVAL method provided satisfactory results when a sufficient carbon coating thickness was applied to the cuttings. It was also observed that the thinner the PVAL layer, the better the quality of the spectra and obtained images in SEM/EDX. Furthermore, the surface of the photographic paper did not seem to be conductive, even after the application of a thick layer of carbon.In conclusion, the Filter method gave the best overall results, but its application required slightly more time and expertise than the two other methods.     

Voltammetric analysis of luminescent markers in gunshot residues

Currently, SEM-EDS is used to detect gunshot residue (GSR) from the presence of Ba, Pb, and Sb in the sample. However, the development of new nontoxic ammunition (NTA) has prevented conventional metals from being found. In this work, we aim to determine the presence of an inorganic luminescent chemical marker based on rare earth in gunshot residues using the technique of squarewave voltammetry (SWV). After firing, the luminescent complex [(Eu₂Zr)(btc)₃(Hbtc)_0.5.6H₂O], which is used as a chemical marker, can be detected under a UV lamp. An aqueous solution with 0.1 mol L⁻¹ KCl as supporting electrolyte can be easily collected on carbon paste electrode surfaces for SWV analysis A = 100 mV, f = 10 Hz, and step potential of 5 mV are required. The luminescent marker incorporated into the carbon paste electrode showed two anodic peak currents in the region of 0.4 V (vs Ag/AgCl) and at 0.75 V (vs Ag/AgCl) and also a cathodic one in 0.4 V (vs Ag/AgCl). SEM-EDS was able to analyze the same voltammetric results for conventional and nontoxic ammunition containing the luminescent marker. Therefore, voltammetry and SEM-EDS are valid for detecting the new residue marker in GSR. Despite this, the electrochemical method is still more advantageous because of its low cost and lack of expensive equipment and supplies in forensic laboratories.     

A comparative study of gunshot residue originating from 9 mm Luger ammunition from various producers

Following previous work on differentiation between gunshot residue according to the type of ammunition used, a specific investigation was undertaken of traces originating from 9 mm Luger ammunition using SEM-EDX. The aim of this study was to determine whether GSR originating from this type of ammunition is similar, or whether differentiation could be made between particular manufacturers of Luger ammunition. The results were collected in the form of counts of particles in each of seven key elemental classes being combinations of lead, antimony and barium. These were then adjusted to a factor known as frequency of occurrence which allows comparison of the distribution of particles within the classes between samples with differences in absolute particle counts. The relationships between the samples were examined using non-parametric statistical tests: R-Spearman and tau-Kendall rank correlation coefficients. It has been found that most of the studied samples of GSR were similar to each other despite their originating from various manufacturers.     

Gunshot residue in Chicago police vehicles and facilities: an empirical study

Suspects in shooting investigations in Chicago are routinely transported in department vehicles and detained in department facilities prior to gunshot residue (GSR) evidence collection. The GSR test results are used to associate the suspect with primary exposure to GSR. The potential for these vehicles and facilities being sources of secondary GSR contamination needed to be determined. A total of 201 samples were collected from randomly selected vehicles and detention facilities. The sampling collected trace materials from surfaces that suspects' hands may contact during the arrest process. These samples were examined for the presence of GSR particles using scanning electron microscopy. Upon completion of the automated analysis, those particles that met an initial GSR screening criterion were relocated and reanalyzed. The locations where GSR particles were recovered allowed us to make recommendations to the Chicago Police Department with regard to transporting and detaining these suspects. The low number of GSR particles recovered suggests that the potential for secondary contamination, although present, is relatively low.     

Visualization of gunshot residue patterns on dark clothing

ABSTRACT: Determination of the muzzle‐to‐target distance is often a critical factor in criminal and civil investigations involving firearms. However, seeing and recording gunshot residue patterns can be difficult if the victim's clothing is dark and/or bloodstained. Trostle reported the use of infrared film for the detection of burn patterns. However, only after the film is developed are the results visible and multiple exposures at different settings may be needed. The Video Spectral Comparator^? 2000 (Foster & Freeman Ltd., Evesham, Worcestershire, U.K.) is an imaging instrument routinely used by forensic document examiners. Without use of specialized film could the VSC 2000 (at appropriate instrument settings) quickly, easily, and reliably provide instantaneous viewing, saving, and printing of gunshot residue patterns on dark and/or blood soaked clothing? At muzzle‐to‐target distances of 6, 12, and 18 in., test fires were made into five different types of dark clothing using eight different handguns of different calibers. Gunshot residues were detected for all eight calibers, and powder burn patterns were seen on dark clothing for all three target distances and calibers except 0.22 long rifle and 0.25 ACP. Bloodstains did not preclude the viewing of these patterns.     

Investigation into the usefulness of DNA profiling of earprints

DNA profiling of biological trace evidence has been used for many years. The application of this technique specifically to the DNA profiling of earprints has not to date been thoroughly investigated. This report presents the results of 60 earprints collected from three healthy adult volunteers under controlled laboratory conditions. DNA profile analysis revealed that high levels of non-donor alleles are observed when earprints are collected for DNA profiling. The source of these non-donor alleles is investigated and the impact that their presence within the profile may have on the use of this technique is discussed.     

Lead isotope measurement of primer gunshot residues and likelihood ratio predictions for forensic cartridge discrimination and individualization in China

Gunshot residues (GSR), cartridge projectiles, and casings are frequently encountered evidence in gun-related forensic investigations. However, in circumstances where the investigation of striation marks is impossible, such as unrecovered or deformed projectiles and cartridge casings, GSR deposited on the hands or clothes of the shooter and victim-related items can provide information to establish a link between the suspect, the firearms used, and the victim. Since the formula of primers used by all cartridge manufacturers in China is identical, links based on the conventional morphological and compositional analysis of GSR are difficult to establish. However, the abundance of lead isotopes in primer components of lead styphnate varies significantly, and a fundamental understanding of these differences may facilitate the validation of primer (p)GSR evidence in forensic investigations. Here, 44 pGSR samples were characterized by Pb isotope ratios of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb using laser ablation multicollector inductively coupled plasma mass spectrometry. There was no obvious mass fractionation of the lead isotope ratios of the primers from individual cartridges analyzed before and after the shooting process, thereby establishing a basis for the comparison of pGSR and unfired cartridges. Evaluation of the results using univariate likelihood ratio (LR) computations revealed low rates of misleading evidence (<0.53%) The results demonstrated that lead isotope ratio analysis of pGSR and LR predictions can provide a practicable method for forensic cartridge discrimination and individualization.     

车辆内接触DNA检测方法的分析比较

目的探讨汽车内接触DNA的分离方法及遗传标记分型效率。方法收集单人长期驾驶的11辆小型轿车,采用粘取法和擦拭法富集方向盘、变速杆和手刹三个部位的脱落细胞,采用磁珠法和硅胶膜法提取基因组DNA,采用GoldenEye^TM 20A和PowerPlex■Fusion进行扩增,并对检验结果进行比较分析。结果方向盘在基因座分型正确率、等位基因drop-in和drop-out基因座比率、单基因座正确率以及单基因座等位基因drop-in和drop-out率六个方面均表现最好,其次为变速杆,最差为手刹;擦拭法和粘取法之间DNA提取在获得的DNA总量和STR检测正确成功率方面无统计学差异;PPFusion与20A的总体基因座分型比较正确率无差异,但单基因座正确率优于20A,drop-out发生率低于20A,drop-in发生率高于20A。结论汽车内脱落细胞的检测可优先采集方向盘部位,根据载体质地选择擦拭法或粘取法采集脱落细胞,选用硅胶膜法或磁珠法提取DNA,PPFusion和20A两个试剂盒均可,分析结果时需特别注意drop-in和drop-out。     

A study of dispersion of gunshot residue from a frequently used Serbian ammunition cal. 7.65 mm to support selected aspects of casework in North Macedonia

The subject of this research was the inorganic gunshot residue component collected from shooting patterns obtained on woven cotton cloth using a Pietro Beretta model 70 pistol, cal. 7.65 mm and Serbian ammunition for the following muzzle-to-target distances: 25, 50, 75, 100 and 125 cm. For each distance, three rounds of shooting were performed. Particles were lifted within a 10 cm radius of the projectile entrance and automatically analyzed using a scanning electron microscope coupled with an energy dispersion X-ray spectrometry. The obtained data on the populations of particles were analyzed taking into account their numbers, chemical classes and sizes. The results showed an apparent maximum incidence within all particles containing barium at about 50 cm distance. Also, lead particles revealed a distinct behaviour, being dominant at a 25 cm distance, falling below the other chemical classes, and finally becoming dominant again at 125 cm. The analysis of the frequency of occurrence of particles sorted according to their sizes confirmed that the small particle population is the largest, and their distribution in function of the equivalent circle diameter is exponential-like. The obtained results provided knowledge on the distribution of particles in the vicinity of the tested firearm and ammunition cal. 7.65 mm which generally corroborates with similarly studied GSR distributions obtained for the use of pistols cal. 9 mm. This information, together with the examinations of gunshot damages and other types of residues such as soot or unburned propellant grains may support qualitative inferences on shooting distance estimation, especially in cases, when the firearm and cartridges are not available to perform test shooting. In such cases even roughly estimated shooting distance can be helpful, e.g. for confirming or excluding the possibility of self-inflicted injuries or suicide and infer on the mutual position of the shooting stage actors. An example of casework that illustrates intermediate shooting distance estimation is presented.     

Volatile organic compounds from the combustion of human and animal tissue

The volatile by-products of the combustion of ordinary fuels such as wood, polystyrene, polyethylene, urethane foam, PVC and the like are well known to the forensic fire debris examiner. When a fire involves a human body, volatile species are produced that are not so well known, including various alkenes and aldehydes. These have sometimes been mistaken for the residues of unusual accelerants. In an attempt to document what volatiles are produced by the combustion of animal fat and human fat, the authors have used an open-tube pyrolysis probe as a microfurnace to burn small samples of unembalmed subcutaneous fat from human, avian and porcine sources, and collect volatiles by charcoal strip adsorption. The volatile products were analyzed by GC/MS. Predominant species included aldehydes in the C6-C10 range, homologous series of alkenes and alkanes, and other hydrocarbon products. These results were compared to those obtained by free-burning (open flame in air) of similar specimens and to the volatiles detected in debris from beneath a human cadaver in a test fire. Differences between the volatile profiles produced by human fat as compared to pork and chicken fat and adventitious sources of such volatiles are discussed.     

The variation in the colour of paint on individual vehicles

The Nanospec 10S microspectrophotometer has been used to study the variations in topcoat colour over the external painted surface of a number of vehicles. The colour differences observed between samples of the manufacturers' original finish topcoats from different points on the vehicles were relatively small. Visual inspection of the reflectance spectra obtained from individual paint layers is a satisfactory method for showing that two layers have the same pigment composition.     

Analysis of Gunshot Residue and Associated Materials—A Review

Abstract: A comprehensive review of the scientific literature on gunshot residue (GSR) is presented. Aspects of both inorganic and organic GSR are discussed, from formation and distribution, to sample collection, preparation, and analysis using a variety of techniques. The interpretation of GSR results is also considered including issues surrounding the contamination, distribution, and transfer of GSR. Potential problems with ulterior sources of GSR like particles have been reported in the literature. For example, particles from environmental and occupational sources have been highlighted as exhibiting similar chemical and morphological characteristics to GSR. These findings are put into context with regard to interpreting samples. A move toward a “case by case” approach is argued to be more preferable to a “formal” classification system where possible. The analysis of both inorganic and organic compositions of residue samples as well as morphological considerations is considered to be a more ideal approach to GSR analysis, whereever practicable.     

Forensic applications of sodium rhodizonate and hydrochloric acid: a new histological technique for detection of gunshot residues

Demonstration of the presence of lead residues deriving from gunshot in skin and underlying tissues is essential for the correct forensic analysis of numerous legal cases. Optical microscopy remains the fastest, cheapest diagnostic technique, even though its sensitivity and specificity are poor because of the scarce quantity of histological tissue that can be examined and possible environmental lead pollution. To confirm the presence of lead from gunshot residues, we applied to histological sections of human skin a technique proposed by Owens and George in 1991 for macroscopic detection of lead on the clothing of shooting victims, involving a reaction with sodium rhodizonate and subsequent confirmation by color change on application of HCl. Our results demonstrate the technical possibility of using this macroscopic technique even on histological samples and support the need for further studies on a larger series of cases correlated with the type of ammunition and firing distance.     

Cognitive biases in the peer review of bullet and cartridge case comparison casework: A field study

ObjectiveForensic judgments and their peer review are often the result of human assessment and are thus subjective and prone to bias. This study examined whether bias affects forensic peer review.HypothesesWe hypothesized that the probability of disagreement between two forensic examiners about the proposed conclusion would be higher with “blind” peer review (reviewer saw only the first examiner’s comparison photos) than with “non-blind” peer review (reviewer also saw the first examiner’s interpretation and proposed conclusion). We also hypothesized that examiners with a higher perceived professional status would have a larger effect on the reported conclusion than examiners with a lower status.MethodWe acquired data during a non-blind and a blind peer review procedure in a naturalistic, covert study with eight examiners (3–26 years of experience). We acquired 97 conclusions of bullet and cartridge case comparisons in the blind and 471 in the non-blind peer review procedure.ResultsThe odds of disagreement between examiners about the evidential strength of a comparison were approximately five times larger (95%-CI [3.06, 8.50]) in the blind than in the non-blind procedure, with disagreement about 42.3% and 12.5% of the proposed conclusions, respectively. Also, the odds that their proposed conclusion was reported as the final conclusion were approximately 2.5 higher for the higher-status examiners than for lower-status examiners.ConclusionsOur results support both the hypothesis that bias occurs during non-blind forensic peer review and the hypothesis that higher-status examiners determine the outcome of a discussion more than lower-status examiners. We conclude that blind peer review may reduce the probability of bias and that status effects have an impact on the peer reviewing process.     

Test for contamination in connection with renovation of post-PCR laboratories

The Teilum building housing the Department of Forensic Medicine at the University of Copenhagen was renovated in 2021/22. All windows were replaced, and the heating system was upgraded. During the renovation, the usual measures to prevent PCR products from escaping the post-PCR laboratories could not be maintained, since construction workers had to move in and out of the rooms carrying tools and debris. Instead, new measures were introduced, that included 1) the construction of a changing room for the workers with immediate access to the post-PCR laboratories, 2) clothing and shoes for the workers, that should only be worn inside the post-PCR laboratories, and 3) strict limitations on the areas the workers could enter, while renovating the post-PCR laboratories. Samples were taken before, during and after the renovation to monitor the possible spread of PCR products from the post-PCR areas. Mixtures of gDNA and PCR products were detected in only three of the 303 samples. All three samples were collected from the post-PCR areas prior to the renovation began, which indicated that the renovation did not cause wide-spread contamination of PCR products.     

Communicating forensic scientific expertise: An analysis of expert reports and corresponding testimony in Tasmanian courts

Forensic criminology examines the use of forensic science in society. Justice can be hampered, for example, if the communication of forensic scientific findings is unclear or misleading, even if unintentionally. Although various recommendations guide the communication of forensic science, it is unclear whether they are reflected in practice. This study explored the communication of forensic biology in 10 cases of major crimes against the person heard in the Tasmanian Supreme Court, where the standard practice is to issue brief summary reports in the first instance. The content of expert reports and corresponding testimony was analysed to determine its adherence to recommendations outlined in standards, practice notes, and research. While reports were found to be very brief, testimony elaborated on all major elements. Mostly elicited by the prosecution, some elements were volunteered by expert witnesses, or raised by defence. Overall, expert evidence in courts—but not reports (due to the use of brief summary reports)—largely adhered to recommendations. Further research is needed to determine the prevalence and effectiveness of alternative approaches to communication that were identified in certain cases.     

Differentiation of bullet type based on the analysis of gunshot residue using inductively coupled plasma mass spectrometry

Porcine tissue samples shot with two different types of bullets, jacketed and nonjacketed, were collected in the fresh state and throughout moderate decomposition. Wound samples were microwave-digested and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) to detect all elements present at measurable levels in gunshot residue (GSR). Elements detected included antimony (Sb), barium (Ba), and lead (Pb), which are considered characteristic of GSR, as well as iron (Fe) and copper (Cu). These five elements were used to differentiate shot tissue and unshot tissue, as well as tissue shot by the two different bullet types, both in the fresh state and throughout moderate decomposition. The concentrations of Cu, Sb, and Pb were able to distinguish the two bullet types in fresh tissue samples at the 95% confidence level. Cu and Pb were able to differentiate the bullet types throughout moderate decomposition at the 99% confidence level.