Identification of GSR on the Shooters Hands Using Energy Dispersive Experiments

Mishra RK¹, Jain P¹, Anil Budania¹, Mukesh Sharma^1* and Tiwari RS^2
*Correspondence: Mukesh Sharma, Physics Division, State Forensic Science Laboratory, Rajasthan, India, Tel: +91-8209791580, Email:

Keywords

Forensic ballistics • GSR • EDX–8000

Introduction

The detection of gunshot residue (GSR) ejected from a gun during its discharge is of great importance in various criminal investigations involving the use of firearms. The analysis of gunshot residue in human tissues and clothing in suicide, homicide or suspicious death provides to the forensic expert valuable information to interpret and reconstruction the scene of occurrences [1]. Forensic analysis has improved significantly over the past few years, mainly owing to the continued increase in the requirement for more reliable results in order to diminish erroneous convictions. GSRs are residues from firearm discharge, and they consist of vapors and particulate materials that are deposited onto the hands (mainly the index fingers and thumbs), face, and clothes of the shooters. If these particles are collected and reliably analyzed, the suspect can be successfully identified. GSRs have three main inorganic elements: lead, barium, and antimony [2]. The analysis of lead from GSRs can be used as an indicator of the presence of the residues. For the assessment of the value of a GSR is linking a suspect and a crime, it is importance to compare two hypotheses: the first can be that of the evidence if the suspect has been shooting in as specific situation, the second that of the evidence if the suspect was not involved in the shooting [3]. Analysis of GSR, Bolck and Stamouli [4] has reported a two level multinomial model for the calculation of the likelihood ratio in order to have a tool to discriminate between same-ammunition-type GSR compositions and different-ammunition-type compositions. Using the two-level multinomial model they reported the conclusion that this model can indeed be applied on such experimental data. Interpretation of GSR data in suspected suicide cases is a difficult task since the victim, who was for sure present in the surroundings of the shooting, may be highly contaminated. On the other hand, the occurrence of false negatives is also quite large. Conducting a follow-up of the study by Molina et al. published earlier [5], Lucas N, et al. [6] have examined the presence of IGSR on the hands of victims of undisputed suicide cases by firearms: 59 cases that occurred in Australia were investigated. About 50% of these cases presented no or very few (less than four) Lead-Barium-Antimony particles, confirming the results of the study conducted by Molina K, et al. [5]. However, most of the cases presenting such low level of characteristic particles were related to the use of 0.22 calibre rifles (the most popular firearm in Australia), for which the primer of the ammunition usually does not contain Antimony. Not surprisingly, this leads to the production of GSR particles with no (or very little) Antimony. Taking such particles into account in the statistics, the number of the cases presenting no or very few (less than four) particles of interest falls down to less than 15%. The article presents other interesting statistics, such as the difference of GSR production as a function of weapon model (i.e. a higher number of GSR particles are produced by revolvers, compared to rifles). Zeichner commented this article, with a discussion about the possible memory effects of the weapon to the contribution of Antimony in IGSR particles [7].

Dona-Fernandez et al. [8] performed an extended comparative study of SEM/EDS and portable laser-induced breakdown spectroscopy. By performing a comparison between data collected from shooters and nonshooters, the authors concluded that even when only one single Lead- Barium-Antimony GSR particle was found by SEM/EDS, the laser-induced breakdown spectroscopy sy.

In a recent study, McKenzie-Coe et al. [9] have presented a novel workflow for the detection of both elemental and organic constituents of the firearm discharge residue from skin swabs using electrospray trapped ion mobility spectrometry coupled to mass spectrometry.

Experimental Set-up

We have used EDX method all samples collected (on cotton, gauze and filter paper) were kept separate and covered with non-conducting material paper foil. The samples were analyzed with an Energy dispersive X-rays Fluorescence instrument – EDX – 8000 (Shimadzu, Germany) equipped with high-performance SDD detector using the simple analysis software (pcedxnavi) general analysis software (pcedx-pro) software provided with the equipment. This software automatically searches all particles that have one of the selected elemental compositions typical of GSR required by ASTM [10]. Though the unit is compact, it is equipped with a large, vacuum-compatible sample chamber. During analysis, the blue led on top is lit, so the instrument status can be checked even from another location. In the system set up bottom irradiation type optical system, in which X-rays are emitted from below the analysis sample [11]. The primary filters, collimators, and sample observation camera are included as standard. When studying the persistence of the GSR population with the EDX analysis by automated search, the primer elements of three new class residues were added to the software program to detect the non-classic GSR on the shooters’ hands resulting from our own research. The control cotton, gauze and filter paper were analyzed with the same automatic procedure adopted to discriminate the background particles from the GSRs collected from hands.

Measurement parameters are tabulated in Table 1, the elemental profile was recorded for any particle by using X-ray spectra with a live time of 360 s for each sample [11].

Sample preparation

The sample preparation phase of present study comprised three experimental scenarios. The decision was taken to simulate contacts and transfers immediately after the firearm discharges had taken place. In the absence of comprehensive studies on the extent and rates of GSR transfer, on hand using country made firearms (pistol and revolver) it was deemed important to ensure that the maximum quantity of GSR available for transfer at the time of contact.

Firearm → Shooter → Cotton Swab/Gauze piece/Filter paper (Buttman)

Across the experimental scenarios, three different materials have been used to pick GSR deposition and transfer were simulated in each sample collection we adopted three different chemically treated cotton swab, gauze piece and filter paper a) with HNO3; b) with Dil. HCl and c) with distilled water, which gives us 09 sample for each study total 21 sample have been analyzed.

Conclusion

The present study provide as specific study of the Country made firearms (Pistol and revolver) particularly found in Indian crime scene. The specific study on GSR for Indian ammunition using country made firearms has not been reported yet. Through our report, the first ever statistics and analysis the GSR using EDX measurement reported in this, which conclude that the main constituents of GSR is consist of Pb-Ba-Sb is verified.

GSR evidence is one of the most common trace evidence examined in crime investigation. GSR examination is done is Forensic Science Laboratory in India with very high accuracy and modern analytical techniques. This study will provide a comparable data to the scientist to take as reference in Indian contest. Significant development in the EDX techniques, the forensic science expert has to be up-to-date with the advancement of the techniques, like SEM-EDX [13], milli-XRF [14] and Synchrotron radiation facility [15]. Now a day’s India is also developing the Synchrotron based source, at CAT, Indore, which will provide the forensic community to analyse trace materials using these facilities.

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