Is it possible to determine firearm calibre and shooting range from the examination of gunshot residue in close range gunshot wounds? An experimental study

© 2013 Anisa Gradašèeviæ et al.; licensee University of Sarajevo Faculty of Health Studies. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. UNIVERSITY OF SARAJEVO FACULTY OF HEALTH STUDIES INTRODUCTION Gunshot residue (GSR) consists of particles composed of antimony, barium and lead that arise from the condensation of primer vapors (1) and also soot debris consisting of carbon and metallic fragments ABSTRACT


INTRODUCTION
Gunshot residue (GSR) consists of particles composed of antimony, barium and lead that arise from the condensation of primer vapors (1) and also soot debris consisting of carbon and metallic fragments Is it possible to determine firearm calibre and shooting range from the examination of gunshot residue in close range gunshot wounds?An experimental study.
from the bullet and cartridge case (2).In the matter of reconstruction of gunshot fatalities, the macroscopic examination of gunshot wounds as well as the investigation of GSR particles gains extensive forensic signifi cance (1,2).Physical and chemical investigations of fi rearm discharge residues are nowadays performed routinely in order to solve a number of forensic problems such as identifi cation of gunshot wounds together with establishing of the entrance and exit (3), estimation of the time since discharge of a fi rearm (4,5), distribution of GSR at the crime scene, estimation of shooting distance (6,7), as well as establishing whether a person has fi red a gun (8).Sensitive analytical methods are required for the identifi cation of inorganic gunshot residues that are usually presented in very small quantities on a substratum, and commonly used methods include atomic absorption spectroscopy (AAS), neutron activating analysis (NAA) (1) , X-ray fl uorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS) (9).Th e aim of the study was determining the type of weapon and shooting distance depending on chemical analysis of inorganic gunshot residue from the skin gunshot wounds in experimental animals (pigs).

METHODS
Experimental study was conducted in order to determine components and their percentage in gunshot residue (GSR).In 60 samples, pig skin was shot by fi ring projectiles from four diff erent weapons and from three diff erent distances, fi ve times from each distances (contact wound, and near contact wound 5 cm and 10 cm).Characteristics of weapons and projectiles are presented in (Table 1).Th e research is performed in accordance with the ethical principles in compliance with the law on the protection of animals in our country.Part of the pig body size is approximately 120 x 45x 20 m composed of skin, subcutaneous and muscle tissue, areas of the chest and abdomen, which is attached to a solid surface.Shooting was conducted using a system for safe fi ring from the fi rearm (Verifi re-Th e Secure Firing Device, Twin Tooling, Canada).Th e weapons used in the experiment were most commonly used in the Balkan region in last 10 years according to Federal and local police.Th e methodology included determining the presence of inorganic material: antimony, barium, lead, nickel, zinc and copper in the skin and subcutaneous tissue using Atomic Absorption Spectrometry (AAS) Inductively Coupled Plasma -Optical Emission Spectrometry (ICP-OES).Samples for chemical analysis were clips of skin and subcutaneous tissue size about 3x3x3 cm, each sample was labeled and packed in a plastic container fi lled with buff ered 10% of formalaldehyde.In order to perform an AAS and ICP-OES analysis and determine content of these elements using an appropriate method, it was necessary to put each sample in the acid-water solution.To achieve this, it was necessary to perform so-called mineralization, i.e. destruction of all organic material.Given the amount of organic matter from several grams (even tens of grams), "mineralization" samples corresponding mineral acids (nitric, sulphuric and hydrochloric) would be completely impractical, because it would require the use of large amounts of these acids.Th is would be a great possibility of contamination of the sample metals (which are, as a rule contained in these acids, regardless of the degree of purity) whose content is determined, and would be increased and the detection limit.Because it is dedicated to the mineralization patterns make burning in platinum dishes.After the process of burning the sample is placed in a bowl incandescent furnace where, at a temperature of 900 o C for 30 minutes, elemental carbon burn completely.Temperature at which the thermal process unfolded mineralization samples were below 1000 o C, which is more than 400 o C temperature below the sublimation of lead oxide, which has a lowest temperature of vaporization or sublimation (1470 o C).Here, based on the realistic assumption that metals whose content determination completely oxidized, as are the non-precious metals, and the samples are accumulated in the form of very fi ne particles (large specifi c surface area), where the whole process of mineralization took place in contact with air.After incineration of elementary carbon, content in the container was moistened with about 1 ml of redistilled water, after which exactly 3 ml of nitric acid (1.65%) very high purity ("Aristar") were added and slightly heated in order to completely dissolve salts.Preliminary measurements were used for calibration, after which fi nal measurements were performed with types of AAS.Contents of lead, copper, zinc and nickel in all solutions samples were determined on fl ame AAS.Due to interference of antimony and barium on fl ame AAS, probably caused by chemical interactions due to its high content of sodium (occurring during atomization in fl ames), we also used ICP-OES which was due to signifi cantly higher temperatures atomisation, resistant to chemical interference.

Statistical analysis
All data were analyzed using the following: descriptive statistics, Kruskal-Wallis one way test, discriminatory equations.P <0.05 was considered signifi cant and p <0.01 was considered highly signifi cant.

RESULTS
Distribution of diff erent percentage of diff erent elements in diff erent types of weapon with regard to shooting distance is presented in Table 2. Since the samples were rather small, due to significant cost of the study, in statistical analysis we used In order to determine diff erences in elements distribution depending on shooting distance within the same type of weapon, we used the Kruskal-Wallis one way test once more (Table 5).Since this analysis has shown that diff erences in elements distribution depending on the shooting distances within the same type of weapon were mainly statistically signifi cant (for 54.17% of cases), we again analyzed it further using statistical discrimination function.Th e analysis showed statistical signifi cance for the all elements again except barium which didn't meet tolerance criteria (canonical correlation 0,669, Eigen value = 0,811, Wilks' Lambda = 0,51, p<0,001), with 58,9% of original grouped cases being correctly classifi ed, which was slightly less reliable compared to weapon type discrimination analysis.Th e following formula for determining weapon type is provided (cutt-off points for diff erent distances are presented in Table 6): We used atomic absorption spectrophotometry (AAS) as a method of gunshot residue particles analysis from gunshot entrance wounds for determining which type of weapon was used in contact or near contact wound.Due to the fact that we have used small number of samples it was necessary to perform discrimination analysis in a way to show the formulas for determining weapon type and shooting distances.Mentioned analysis showed that formulas for determining types of weapon were precise in nearly 80% of cases.

DISCUSSION
Gunshot residue particles form during the discharge of a fi rearm.As the fi ring pin strikes the primer cap, the primer mixture is ignited, creating an environment of rapid temperature and pressure increases within the cartridge.Th is increase in temperature melts the primer mixture and within a few milliseconds the vaporization points of lead (Pb), barium (Ba), and antimony (Sb) are exceeded (Pb 1620/C, Ba 1140/C, Sb 1380/C).Th e eff ects of supersaturation cause vaporized particles to condense back onto the liquefi ed primer surface as droplets.Th ere has been evidence to suggest that inorganic GSR particles of materials originating solely from the primer Pb (lead), Cu (copper), Zn (zinc), Ni (nickel), Sb (antimony), Ba (barium)  (primer GSR) are formed even before the propellant is ignited.As the primer mix ignites the propellant powder, a second rapid increase in pressure and temperature occurs and the bullet is expelled from the fi rearm barrel.During this process, the particles involved are subjected to extreme temperature and pressure is followed by rapid cooling.Particles form as liquid droplets, which subsequently solidify (11).Th e areas from which GSR may be collected are wide ranging.Skin, vehicles (seats and seat backs, doors, windows, dashboards, headliners, interiors, and exteriors), the surroundings of an incident, doors, windows, body parts, clothing, and any surfaces in the immediate vicinity of a fi rearm discharge may all be sample targets (11).We analyzed these components in gunshot entrance wound.When the reconstruction of gunshot fatalities is in question, the macroscopic examination of gunshot wounds as well as the investigation of GSR particles gains extensive forensic signifi cance (1).Gunshot analysis has been widely studied in the forensic literature for the estimation of the fi ring range and in the last decades a lot of techniques have been used for the detection and identifi cation of GSR particles in the gunshot wound (11).Th ese experiments have clarifi ed that the amount is strictly correlated to the shooting distance (2,12,13).Th ere are many histochemistry (12)(13)(14)(15) studies and electron microscopy methods who are accurate and precise for estimating fi ring distance (16,17).However, most of these studies, if not all of them, are not applicable in every day forensic work, mostly due to their cost, as well as a necessity for sophisticated and expensive equipment.
A lot of diff erent methods in GSR analyzing have been used (3,11), but only a few of them dealt with analyzing gunshot wounds.In one of them, gunshot wounds from previously amputated human parts, both normal and charred, were used in analysis with micro CT, and the conclusion was that this analysis could provide the diff erential diagnosis between gunshot and sharp force wounds, entry and exit holes (1, 2) artefacts and gunshot lesions.In another study by the same authors, micro CT analysis was conducted on fresh and decomposed gunshot wounds, suggesting it could be useful screening tool for diff erentiating entrance from exit wounds (18).Other authors analyzed GSR in gunshot wounds using confocal laser scanning microscopy (13), or radiochemical neutron activation analysis (19).Regardless of the good results of these studies in analyzing gunshot wounds, these types of methods and devices (such as micro CT, confocal laser scanning microscopy, neutron activation analysis etc.) are often neither accessible, nor aff ordable in everyday forensic practice.
In practical work diff erent diffi culties and controversies may arise in forensic evaluation of gunshot wounds, which may include estimation of calibre, shooting distance, and sometimes even estimation of whether the wound is entrance or exit may be diffi cult.Our presented method in GSR analysisatomic absorber spectrophotometry (AAS) in the close range entrance gunshot wounds could bridge these diffi culties.Th is method is easily available, relatively cheap and practicable.In the case where   we have small samples and diff erences in elements distributions which were depending of type of weapon within the same shooting distances, we can use discriminant functions.It could provide help in determining the type of weapon (of four diff erent weapons in our study) with relatively good precision (nearly 80%, or in 4 out of 5 cases).Th is gives rise to the possible weakness of our study, since we have examined for the most commonly used weapons in the Balkans' region.In other regions and parts of the world, the other types of weapons are possibly used, which could be the possible subject for some future studies.Although all the examined cases were in close range shots (contact, 5 cm, 10 cm).Th is method could be helpful in determining whether the gunshot wound is contact or near contact, even though with slightly lesser precision (nearly 60%, or in 3 out of 5 cases).
Th is analysis could be especially useful in cases where for some reason it is not easy to determine whether the gunshot wound is entrance or exit.One of such situations could be in cases of postmortally putrefi ed bodies.Putrefaction changes will eventually dissolve all of the body's soft tissues and organs, to an extent that even makes them unrecognizable (19).However, inorganic materials such as examined metals (lead, copper, zinc, nickel, antimony and barium) remain unchanged and therefore they could be further analyzed, regardless of the putrefaction changes.Th is could be particularly useful in cases where missile trajectory only involves only soft tissue.Another possible application of this method could be in charred bodies with gunshot injuries, or even in some cases in fresh bodies when it's not easy to macroscopically diff erentiate entrance from exit wound.

CONCLUSION
Th e presented study showed that chemical analysis of GSR in entrance wound with atomic absorber spectrophotometry could be useful in determining the type of weapon, as well as the shooting distance, i.e. in our study, suggesting whether the wound is contact or near contact.Th is could be particularly useful in postmortally putrefi ed or charred bodies with gunshot wounds.Th e limitation of this survey is that it is based on most commonly used weapons in the Balkans' region, and therefore its applicability to other regions must be taken cautiously, also another limitation of the study, is small sample, but we think this could be a subject for the future studies.

TABLE 1 .
Weapons used in the experiment

TABLE 3 .
Kruskal-Wallis one way test to determine differences in elements distribution depending on type of weapon within the same shooting distance

TABLE 4 .
Cutt-off points for different weapons

TABLE 5 .
Kruskal-Wallis one way test in order to analyze differences in elements distribution depending on the shooting distances within the same type of weapon

TABLE 6 .
Cutt-off points for different shooting distances