Forensic veterinary radiology: ballistic-radiological 3D computertomographic reconstruction of an illegal lynx shooting in Switzerland

The most popular handgun in Brazil is the single round-barrel caliber 0.38 revolver. In recent years, however, owing to the modernization of police arms and their availability on the legal and illicit markets, pistols have become increasingly popular and currently represent about 20% of police seizures. In a previous paper we presented a novel collection method for gunshot residues (GSR) using a sampling procedure based on ethylenediamine-tetraacetic acid (EDTA) solution as a complexing agent on moistened swabs with subsequent detection using sector field-high resolution-inductively coupled plasma-mass spectrometry (SF-HR-ICP-MS). In the present paper, we discuss the capability of this methodology to identify antimony (Sb), barium (Ba) and lead (Pb) on the hands of volunteers after shot tests with 9 mm and 0.40 in. caliber pistols. Two types of munitions were tested: 9 mm Taurus and clean range. The use of a technique with high sensitivity, such as SF-HR-ICP-MS, permits the identification of low concentrations (less than 1 microg/L) of metals in firearm residue and constitutes a powerful tool in forensic science. We also discuss the importance of the sampling procedure, including collection from a different body part than the gun hand of the suspect. Comparison of the analytical data obtained allows clear discrimination between samples from the hands of shooters and non-shooters.     

The accelerated polyvinyl-alcohol method for GSR collection--PVAL 2.0

The polyvinyl-alcohol collection method (PVAL) is used in forensic practice to gather topographical information about gunshot residues (GSR) from the hands to decide if the subject has made use of firearms. The results allow a distinction between suicide and homicide. The only inconvenience of PVAL was that the procedure took about 60 min because three layers of liquid PVAL had to be applied and dried. Therefore, the collection method was only applied to corpses. The improved and accelerated PVAL 2.0 uses a sandwich technique. Cotton gauze for stabilization is moistened with a 10% PVAL solution. A solid film of PVAL (Solublon) is spread on the cotton mesh. The gauze is then modeled to the hand and dried with a hair dryer. After removing the cotton gauze, the traces are embedded in the water-soluble PVAL. The procedure does not take more than 15 min. The results demonstrate the qualities and advantages of PVAL: topographical distribution of GSR, highest gain of GSR, sampling of all other traces like blood, backspatter etc., and humidity does not reduce the gain. In addition, with the new PVAL 2.0 dislocation of GSR or contamination are excluded. PVAL 2.0 can also be applied on live suspects.     

A method for enhancing gunshot residue patterns on dark and multicolored fabrics compared with the modified Griess test

In using infrared or infrared-enhanced photography to examine gunshot residue (GSR) on dark-colored clothing, the GSR particles are microscopically examined directly on the fabric followed by the modified Griess test (MGT) for nitrites. In conducting the MGT, the GSR is transferred to treated photographic paper for visualization. A positive reaction yields an orange color on specially treated photographic paper. The examiner also evaluates the size of the powder pattern based on the distribution of nitrite reaction sites or density. A false-positive reaction can occur using the MGT due to contaminants or dyes that produce an orange cloud reaction as well. A method for enhancing visualization of the pattern produced by burned and partially unburned powder is by treatment of the fabric with a solution of sodium hypochlorite. In order to evaluate the results of sodium hypochlorite treatment for GSR visualization, the MGT was used as a reference pattern. Enhancing GSR patterns on dark or multicolored clothing was performed by treating the fabric with an application of 5.25% solution of sodium hypochlorite. Bleaching the dyes in the fabric enhances visualization of the GSR pattern by eliminating the background color. Some dyes are not affected by sodium hypochlorite; therefore, bleaching may not enhance the GSR patterns in some fabrics. Sodium hypochlorite provides the investigator with a method for enhancing GSR patterns directly on the fabric. However, this study is not intended to act as a substitute for the MGT or Sodium Rhodizonate test.     

Stubs Versus Swabs? A Comparison of Gunshot Residue Collection Techniques

Abstract: The collection efficiency of two widely used gunshot residue (GSR) collection techniques—carbon‐coated adhesive stubs and alcohol swabs—has been compared by counting the number of characteristic GSR particles collected from the firing hand of a shooter after firing one round. Samples were analyzed with both scanning electron microscopy and energy dispersive X‐rays by an experienced GSR analyst, and the number of particles on each sample containing Pb, Ba, and Sb counted. The adhesive stubs showed a greater collection efficiency as all 24 samples gave positive results for GSR particles whereas the swabs gave only positive results for half of the 24 samples. Results showed a statistically significant collection efficiency for the stub collection method and likely reasons for this are considered.     

Combined Collection and Analysis of Inorganic and Organic Gunshot Residues

Gunshot residue (GSR) analysis and their interpretation provide crucial information on a criminal investigation involving the use of firearms. To date, several approaches have been proposed for the implementation of a combined sampling and analysis of inorganic (IGSR) and organic GSR (OGSR). However, it is not clear at this stage if concurrent analyses of both types of residue might be detrimental to the analysis of IGSR currently applied in forensic laboratories. Thus, this work aims to compare and evaluate three different protocols for the combined collection and analysis of IGSR and OGSR. These methods, respectively, involve the use of a modified stub (with two halves, one for the detection of IGSR and the other for the analysis of OGSR); the sequential recovery of GSR with two stubs mounted with different adhesives (double-sided carbon tape and Tesa® TACK) and the sequential analysis of IGSR and OGSR from a single carbon stub following carbon deposition. The detection of IGSR was carried out using SEM-EDX, while OGSR analysis was performed using ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS). Obtained results for experiments performed using Geco Sinoxid^® ammunition indicated that sequential analysis was the most suitable protocol for the combined collection and analysis of both IGSR and OGSR. A higher number of inorganic (characteristic and consistent) particles and higher concentrations of ethylcentralite, N-nitrosodiphenylamine, diphenylamine, and nitroglycerin were recovered with this method.     

The Effect of Skin Debris on Gunshot Residue Sampling and Detection

These experiments were designed to determine whether skin debris (desquamated epithelial cells and apparent skin oils) affects gunshot residue (GSR) particle detection on the sticky tape lift samples prepared for scanning electron microscopy (SEM). A dabbing experiment showed that GSR particles accumulate not only on the adhesive surface of the sampler, but also on the epithelial cell surfaces. Samplers were loaded with target GSR followed by dabbing 30 times on the back of a hand. Backscatter electron images were taken at 20 kV and for some at 30 kV of the same areas. The samplers were then treated with a sodium/calcium hypochlorite solution (bleach) to remove skin debris and again imaged in the SEM. Comparison of these images shows more GSR particles will likely be revealed at 30 kV than 20 kV and more particles revealed by the bleach treatment in an automated SEM system.     

A simple method for detection of gunshot residue particles from hands, hair, face, and clothing using scanning electron microscopy/wavelength dispersive X-ray (SEM/WDX).

We devised a simple and rapid method for detection of gunshot residue (GSR) particles, using scanning electron microscopy/wavelength dispersive X-ray (SEM/WDX) analysis. Experiments were done on samples containing GSR particles obtained from hands, hair, face, and clothing, using double-sided adhesive coated aluminum stubs (tape-lift method). SEM/WDX analyses for GSR were carried out in three steps: the first step was map analysis for barium (Ba) to search for GSR particles from lead styphnate primed ammunition, or tin (Sn) to search for GSR particles from mercury fulminate primed ammunition. The second step was determination of the location of GSR particles by X-ray imaging of Ba or Sn at a magnification of x 1000-2000 in the SEM, using data of map analysis, and the third step was identification of GSR particles, using WDX spectrometers. Analysis of samples from each primer of a stub took about 3 h. Practical applications were shown for utility of this method.     

Screening of gunshot residues using desorption electrospray ionisation-mass spectrometry (DESI-MS)

Several studies have indicated that there are potential environmental sources of particles resembling inorganic primer found in gunshot residues (GSR); as a consequence examiners are reluctant to unambiguously assign the origin of inorganic particles. If organic gunshot residues (OGSR) were found in combination with inorganic particles, the possibility of environmental sources could be potentially eliminated, thereby significantly enhancing the strength of the evidence. Methods have been previously described whereby GSR specimens can be analysed for the presence of OGSR or inorganic GRS (IGSR). However, no methods have been reported that allow the analysis of both OGSR and IGSR on the same specimen. Described in this article is a direct method using desorption electrospray ionisation-mass spectrometry (DESI-MS) for the detection of methyl centralite (MC), ethyl centralite (EC) and diphenylamine (DPA) on adhesive tape GSR stubs typically used for scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) analysis. The optimisation of numerous parameters was conducted using an experimental design. The results indicate that direct analysis of these organic components of GSR is possible although some limitations were also identified. This initial investigation has also indicated that subjecting stubs to DESI analysis does not interfere with subsequent SEM-EDX analysis of primer residues; therefore the technique described herein allows a comprehensive examination of GSR that would be highly probative in the event that both OGSR and IGSR are detected in the same specimen.     

Gunshot residue testing in suicides: Part II: Analysis by inductive coupled plasma-atomic emission spectrometry

Several different methods can be employed to test for gunshot residue (GSR) on a decedent's hands, including scanning electron microscopy with energy dispersive x-ray (SEM/EDX) and inductive coupled plasma-atomic emission spectrometry (ICP-AES). In part I of this 2-part series, GSR results performed by SEM/EDX in undisputed cases of suicidal handgun wounds were studied. In part II, the same population was studied, deceased persons with undisputed suicidal handgun wounds, but GSR testing was performed using ICP-AES. A total of 102 cases were studied and analyzed for caliber of weapon, proximity of wound, and the results of the GSR testing. This study found that 50% of cases where the deceased was known to have fired a handgun immediately prior to death had positive GSR results by ICP/AES, which did not differ from the results of GSR testing by SEM/EDX. Since only 50% of cases where the person is known to have fired a weapon were positive for GSR by either method, this test should not be relied upon to determine whether someone has discharged a firearm and is not useful as a determining factor of whether or not a wound is self-inflicted or non-self-inflicted. While a positive GSR result may be of use, a negative result is not helpful in the medical examiner setting as a negative result indicates that either a person fired a weapon prior to death or a person did not fire a weapon prior to death.     

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.     

GSR2005--continuity of the ENFSI proficiency test on identification of GSR by SEM/EDX.

Within the framework of the ENFSI Expert Working Group "Firearms" a proficiency test on the detection and identification of GSR by energy-dispersive scanning electron microanalysis (SEM/EDX) is carried out in a 2 years term. The latest test was performed in 2005/2006 and was denoted as GSR2005. Seventy-five laboratories from 28 countries participated in this proficiency test and submitted in total 83 independent data-sets. The participating laboratories were requested to determine the total number of PbSbBa containing particles on a synthetic test sample following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. Furthermore size and position of the detected particles had to be reported by the laboratories and were evaluated statistically. The results were compiled by means of z-scores according to the IUPAC and EURACHEM guidelines-assessing individual laboratory achievements (inter-laboratory) as well as intra-laboratory performance-and were compared to the results of the previous proficiency test run GSR2003 (1). The comparison shows that there is a noticeable improvement in the method's detection capability.     

Particle Analysis for the Detection of Gunshot Residue (GSR) in Nasal Samples Using Scanning Laser Ablation and Inductively Coupled Plasma-Mass Spectrometry (SLA-ICPMS)

Currently, aluminum stub with carbon adhesive devices are used to collect inorganic gunshot residues (GSR) from the hands of a shooter. In an ideal shooting case, the gunshot particles do not persist for more than 2 h in the hands of the shooter, provided that the hands have not been washed. However, for forensic analysis and inference, the extended persistence of GSR would be desirable. This study investigates a novel GSR sampling and detection protocol. Sampling was performed in the nostrils using swab devices impregnated in ethylenediaminetetraacetic acid (EDTA). The GSRs persisted for longer periods in nasal mucus than on the hands, and particles were detected 6 h after shooting occurred. The analytical determination was conducted by scanning laser ablation-inductively coupled plasma-mass spectrometry (SLA-ICPMS) which enable the identification of the number of particles and their elemental composition. Seventeen isotope signals corresponding to ¹³C, ²⁰⁵Tl and 15 analytes that are usually associated with the composition of GSR residues were monitored: ²⁷Al, ²⁹Si, ³¹P, ³³S, ³⁵Cl, ³⁹K, ⁴⁴Ca, ⁵⁷Fe, ⁶⁰Ni, ⁶³Cu, ⁶⁶Zn, ¹¹⁸Sn, ¹²¹Sb, ¹³⁷Ba, and ²⁰⁸Pb. The SLA technique enabled the reduction of the swab analysis time to 40 min. The effectiveness of this methodology was evaluated with two types of firearms: a pistol and a shotgun. The results indicated that the methodology proposed for the analysis of the nasal GSR was effective and that it can improve or complement the forensic analyses and inferences presented in a court.     

GSR2005—Continuity of the ENFSI Proficiency Test on Identification of GSR by SEM/EDX

Abstract:  Within the framework of the ENFSI Expert Working Group "Firearms" a proficiency test on the detection and identification of GSR by energy-dispersive scanning electron microanalysis (SEM/EDX) is carried out in a 2 years term. The latest test was performed in 2005/2006 and was denoted as GSR2005 . Seventy-five laboratories from 28 countries participated in this proficiency test and submitted in total 83 independent data-sets. The participating laboratories were requested to determine the total number of PbSbBa containing particles on a synthetic test sample following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. Furthermore size and position of the detected particles had to be reported by the laboratories and were evaluated statistically. The results were compiled by means of z -scores according to the IUPAC and EURACHEM guidelines—assessing individual laboratory achievements (inter-laboratory) as well as intra-laboratory performance—and were compared to the results of the previous proficiency test run GSR2003 ( 1 ). The comparison shows that there is a noticeable improvement in the method's detection capability.     

Detection of Pb,Ba, and Sb in Cadaveric Maggots and Pupae by ICP-MS*

The concentrations of lead (Pb), barium (Ba), and antimony (Sb), characteristic of GSR, were determined in soil sediments and immature (larvae) of cadaveric flies of the family Calliphoridae, by inductively coupled plasma mass spectrometry (ICP-MS). This research refers to a case study from two real crime scenes in which the corpses were in an advanced state of decomposition. In case 1, the victim had holes similar to gunshot wounds, and in case 2, there was no evidence of perforations in the corpse. Soil sediment collection was performed at three different points of the terrain, at a minimum distance of 10 m from the corpse, for cases 1 and 2. In relation to the collection of immatures, larvae were collected in regions of the mouth, nose, and orifices similar to the entry of firearms projectile into the body, for case 1, and collection of larvae and pupae, located on the body and underneath it, for case 2. It was possible to detect and quantify the three elements of interest (Pb, Ba, and Sb) by ICP-MS in both sediment and cadaveric larvae. Concentrations of 4.44, 8.74, and 0.08 μg/g were obtained for Pb, Ba, and Sb, respectively, in the soil for case 1. For the case 2, the concentrations in Pb, Ba, and Sb were from 16.34 to 26.02 μg/g; from 32.64 to 57.97 μg/g and from 0.042 to 0.30 μg/g, respectively. In the larvae, Pb, Ba, and Sb were quantified in cases 1 and 2 with a concentration of 6.28 and 1.78 μg/g for Pb, 1.49 and 2.94 μg/g for Ba, 0.50 μg/g and <LD for Sb, respectively. These new results present the detection of characteristic elements of GSR in cadaveric larvae in humans in a real crime scene, besides highlighting the importance of the study of immature flies, using the ICP-MS technique in forensic analysis.     

Differential pulse anodic stripping voltammetry of lead and antimony in gunshot residues

Differential pulse anodic stripping voltammetry (DPASV) using a glassy carbon/mercury film electrode (GC/MFE) has been applied for characterization and quantitative detection of gunshot residues (GSR). This technique allows for simultaneous detection of Pb and Sb from GSR hand swabs that is simple, fast, and non-destructive. The use of a KNO₃/hydrazine sulfate matrix, instead of HCl, reduces possible interferences and allows for a small sample size to be used in analysis but yielding greater sensitivity.     

Evaluation of the Simultaneous Analysis of Organic and Inorganic Gunshot Residues Within a Large Population Data Set Using Electrochemical Sensors*,†

The increasing demand for rapid methods to identify both inorganic and organic gunshot residues (IGSR and OGSR) makes electrochemical methods, an attractive screening tool to modernize current practice. Our research group has previously demonstrated that electrochemical screening of GSR samples delivers a simple, inexpensive, and sensitive analytical solution that is capable of detecting IGSR and OGSR in less than 10 min per sample. In this study, we expand our previous work by increasing the number of GSR markers and applying machine learning classifiers to the interpretation of a larger population data set. Utilizing bare screen-printed carbon electrodes, the detection and resolution of seven markers (IGSR; lead, antimony, and copper, and OGSR; nitroglycerin, 2,4-dinitrotoluene, diphenylamine, and ethyl centralite) was achieved with limits of detection (LODs) below 1 µg/mL. A large population data set was obtained from 395 authentic shooter samples and 350 background samples. Various statistical methods and machine learning algorithms, including critical thresholds (CT), naïve Bayes (NB), logistic regression (LR), and neural networks (NN), were utilized to calculate the performance and error rates. Neural networks proved to be the best predictor when assessing the dichotomous question of detection of GSR on the hands of shooter versus nonshooter groups. Accuracies for the studied population were 81.8 % (CT), 88.1% (NB), 94.7% (LR), and 95.4% (NN), respectively. The ability to detect both IGSR and OGSR simultaneously provides a selective testing platform for gunshot residues that can provide a powerful field-testing technique and assist with decisions in case management.     

Environmental assessment of gunshot residue particles in the public domain of the United Kingdom

Only limited data currently exists on the inadvertent transfer of gunshot residue (GSR), or GSR-like particles through contact with public places. In this study, an assessment occurrence of GSR in public environments in England, UK was undertaken. Utilizing a stubbing sampling technique over 260 samples were collected from areas accessible to the public, including buses, trains, taxis, and train stations. Stub analysis was performed by Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM-EDX). The results showed no characteristic GSR particles were detected on any of the 262 samples taken. From these samples, a total of four indicative/consistent particles were identified on one train seat (2× BaAl, 2× PbSb). Although geographical location and firearm association is likely to influence GSR occurrence, the data suggests that the potential for inadvertent GSR transfer through contact with public transport and associated communal areas is insignificant. Further research assessing environmental background levels of GSR in additional geographical locations is critical in an evaluation of the potential for GSR transfer from the environment.     

Transfer and Distribution of Gunshot Residue through Glass Windows

Research into the deposition patterns of primer gunshot residue (GSR) beyond a primary target was previously nonexistent. This study aimed to determine the deposition patterns of GSR once a bullet passed through an initial target and continued on its path into additional targets. Multiple repetitions were performed to assess the GSR deposition patterns after a bullet was shot through a closed window into either a dummy or a wall within an enclosed room. Samples were taken from both the primary and secondary target holes as well as from nontarget areas. Significant amounts of GSR were found on all samples. The results show that GSR continues to be deposited along the path of the bullet after passing through a primary glass target. These findings reiterate the lack of probative value in collecting GSR samples from gunshot victims even if they are in an enclosed area separate from the shooter.     

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.