microscopic and microanalytical examinations of metallic particles

Microscopic and microanalytical examinations of metallic particles and single textile fibres for forensic purposes

Z. Brozek-Mucha 1,2 and J. Was-Gubała1,2 1 Department of Criminalistics, Institute of Forensic Research, Westerplatte St. 9, 31-033 Krakow, Poland 2 Faculty of Chemistry, Jagiellonian University, Ingardena St.3, 30-060 Krakow, Poland

Metallic particles and textile fibres belong to forensic microtraces of a distinctively high evidential value. Examinations of these materials performed by various techniques of optical microscopy, electron microscopy, x-ray microanalysis and other microspectroscopic methods are utilised mainly for their identification and comparison to reference materials secured as evidence in various crimes. Results of such examinations are complementary to other information obtained during investigations and can be used to crime reconstruction. In shooting incidences usually gunshot residues, among them characteristic metallic particles, are cautiously studied. However, our experience demonstrates that detailed examinations of fibres in the surroundings of a gunshot damage in clothing of victims may additionally contribute to explanation of the impact done to the clothing and so significantly improve the inferences on the crime reconstruction. This is illustrated by an example of complex examinations of both, gunshot residues and textile fibres, selected from the casework of the authors.

Keywords forensic sciences; forensic chemistry; metallic particles; gunshot residues, textile fibres; optical microscopy; scanning electron microscopy; x-ray microanalysis, UV/Vis microspectrophotometry, FTIR microspectroscopy; Raman microspectroscopy

1. Introduction

Contemporary microscopic and microanalytical methods play a growing role in forensic sciences, e.g. in forensic chemistry as they enable a scientist to investigate nano- and picogram amounts of materials, usually called microtraces, present in the surroundings of human being that may became an evidence in trial. Among many materials subjected to forensic examinations metallic particles, e.g. gunshot residues and fragments of the single textile fibres reveal exceptionally high evidential value, especially when they are of rare origin or bear traces of different damages. Although different in nature, the two kinds of traces: textile fibres and gunshot residues (GSR), ought to be characterised by microscopic and microanalytical methods, such as several methods of light microscopy (e.g. stereomicroscopy, polarized light, comparison, fluorescence, and interference), microspectrophotometry in the UV and visible range for objective colour analysis and comparison of fibres, micro-FTIR spectroscopy, micro-Raman spectroscopy, scanning electron microscopy and x-ray spectrometry. The final interpretation of the analytical results depends on a number of factors: particular circumstances of the event, the way in which the evidence was gathered at the crime scene, the precision of the laboratory tests, the chemical content and morphology of GSR, the colour and type of fibres recovered, and the measurable effects of destructive processes can all enhance or lessen the evidential value of such material. In addition, the robustness of the analytical data interpretation often demands conducting special scientific research of relationships between the features of the traces and various factors influencing their prevalence and persistence. Solution to any particular forensic problem may contribute to a crime reconstruction as well as explanation of historical mysteries. Complex studies towards the cause of textile damages, including possible presence of GSR, were performed together with medical, genetic and toxicological examinations in order to establish the cause of the death of general Wladyslaw Sikorski, the Prime Minister of the Polish Government in Exile, being also a Commander-in-Chief of the Polish Armed Forces as well, deceased in Gibraltar on the 4th of July, 1943 in result of an airplane catastrophe [1, 2]. In the course of our studies the identification of garments and other textile products, as well as various materials, e.g. fragments of metals and chemical substances found in the coffin by the body was carried out. The articles of clothing revealed no damages that could have resulted from a thermal factor, such as fire, high temperature or explosion. Mechanical damages of fabric and knitted fabric resulted from annealing processes and biodegradation of the textile products. Metallic particles present near the body were fragments of the solder sealing the cover with the coffin. Finding no parts of an ammunition and no gunshot residues complied with the autopsy examinations. Thus, a gunshot, an explosion or a fire-raising were excluded as the cause of the general’s death [3].

Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)

© 2012 FORMATEX 1480

2. Metallic particles

Metallic particles originating from the primer of a firearm cartridge that dissipate in the vicinity of a shooting person are characterised by their exceptional chemical content and morphology demonstrating features of molten and suddenly cooled matter (Fig. 1). That makes them distinguishable from particles of other sources and accounts on their high value in relating a person with the fact of using a firearm. However, examined together with residue of the propellant and other parts of the cartridge as well as with the impact made on human skin and textiles by shooting, they may also be very informative in other aspects of shooting incidence investigations, e.g. in differentiation of entry and exit wounds and damages in textiles and leathers, estimation of the shooting distance, establishing the kind of ammunition used and tracing the trajectory of a projectile. Samples of gunshot residue can be collected from hands, face, hair and clothing of the suspects and the victims of a shooting incidence as well as from many other substrates depending on the investigated circumstances of the incident.

a) b)

Fig. 1 Typical gunshot residue collected from: a) hands of a shooter, b) interior of a case of a discharged cartridge (backscattered electron image, magnification 2500 x). Despite the rapid developments in methods of instrumental analysis and useful protocols being recently worked out by forensic chemists for detection of GSR, there still remain many challenges. Therefore, detailed study have been recently undertaken for better understanding of the mechanism of formation and dispersion of particles in the surroundings of the shooting gun as well as their interactions with a substrate and so their persistence and prevalence in the human environment.

2.1 Relating a person to a shooting incident

To prove that a person was present in a close vicinity of a firing gun, GSR ought to be characterised by both, the specific element content being related mainly to the composition of the primer mixture and their morphology. The most popular method simultaneously providing information on the two features is scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDX) [4-6]. Automation of the analytical process of GSR examinations with this method was successfully solved helping an operator in the arduous process of location and chemical classification of particles [7]. SEM-EDX systems are nowadays able to detect submicron particles and the quality of their performance in GSR search can be measured by means of artificial test sample fulfilling the requirements of standards ISO 5725 and ISO 13528 [7]. According to the obtained list of particles, comprising data on their size, morphology, position on the sample for manual relocation, etc. as well as the corresponding X-ray spectra and images stored, particles are classified into three different categories: ‘GSR characteristic’, ‘consistent with GSR’ and environmental particles, respectively. Evaluation of the obtained data and formulation of the expert’s opinion requires, however, an additional information on the chemical composition of the primer, the elemental contents and morphology of gunshot residue, a knowledge on the possibilities of detection of such particles, both on users and non-users of firearm, i.e. on their prevalence [8] as well as information on the persistence of the particles on various substrates of the shooting person.

2.1.1 Persistence of GSR

Studies on the persistence of gunshot residue concentrated mainly on the shooter’s hands due to the fact that the greatest amounts of particles settle on the shooter’s hands [9, 10]. With time, however, they are being rapidly lost, thus in cases, when the suspect is not being apprehended immediately after shooting, but few hours later, samples from other substrates, such as his clothing or, much less frequently, his face and hair, is being collected. Usefulness of securing the external clothing of the suspects as the evidence in shooting cases complies with case experience of the Institute of Forensic Research, Krakow. Also, the experience of the Israeli Police has shown that procedure of collecting samples not only from the shooter’s hands, but also from his clothing and hair has been found successful in obtaining positive results for samples collected from hair and clothing of the suspects, even when samples from his hands were found negative [11]. Therefore, detailed examinations of the persistence of gunshot residue, simultaneously collected from



hands, face and hair, and clothing of the shooting person, were recently performed [12]. Samples were collected from 5 shooters in 9 time intervals after a single shoot with a Luger 9mm pistol, in the range of 0 – 4h and examined with scanning electron microscopy and energy dispersive X-ray spectrometry. Numbers of particles, frequencies of occurrence of certain compositions of particles and their sizes in function of the time intervals were inspected. The greatest numbers of particles were observed in samples collected from hands right after shooting, but they fall down quickly with time. In samples collected from the face smaller initial numbers of particles were found, but they lasted at similar level longer. The estimated half-life times of particles were less than 1h for samples taken from hands, over 1h for clothing and about 2 – 3h for face. In samples collected in longer intervals after shooting there were present particles of small sizes and irregular shapes. The obtained results demonstrated that including the evidence collected from the suspect’s face and hair may increase the probability of detection of gunshot residue in cases, when the suspect hasn’t been apprehended immediately after the investigated incident.

2.1.2 Contamination with GSR

From the examinations of 100 people group of volunteers the level of GSR contamination for various occupational environments in Poland was established by one of us (ZBM). In samples collected from hands of 55 people declaring no contact with weapons GSR were absent, but in the group of 45 police officers and hunters in samples taken from hands of 19 people the presence of 1 to 27 characteristic particles Pb-Sb-Ba was established. However, using the low-risk-criterion, i.e., at least 5 hours between last shooting and collecting samples, 15 out of 16 police officers (94%) had no GSR and 8 out of 10 hunters (80%) were free from contamination with Pb-Sb-Ba particles. This study empirically supported the intuitive expectation that characteristic GSR particles are related to the time and place of a gunshot and additionally proved that high value of GSR as an evidence of participation in a shooting incident.

2.1.3 Metallic particles similar to GSR

The interpretation of the analytical findings within forensic examinations of GSR requires also consideration of alternative sources of particles similar to GSR. Whereas it has been found that environmental particles originating from lighter flint, fireworks and car break pads remain of low risk to be mistaken for GSR [8, 13], there are not many works on welding, as a potential source of spherical particles containing metals, such as aluminium or titanium, being also components of primers in lead-free ammunition. Thus, a study of the chemical and morphological features of particles originating from welding of steel and aluminium was undertaken (by ZBM) for their comparison with GSR. The subject of the study were samples of the covering of 10 electrodes of rutile, rutile-cellulose, alloyed and alkaline types as well as samples of micro-traces collected from the welders’ gloves after welding steel and aluminium (11 samples).The collected materials were examined by means of SEM-EDX method. In the samples originating from both, steel and aluminium welding, there are present spherical particles of the metals being welded (Fig. 2), the covering of the electrodes (titanium and other light elements) as well as particles with partially crystallised iron oxide on their surface (Fig. 3). The effective circle diameters of the detected particles were in the range of tens of micrometres, while the diameter of the majority GSR is about 1 micrometer.

a) b)

Fig. 2 Welding particles: a) titanium (darker part) merged with iron (lighter part) originating from welding of steel objects with the use of a rutile electrode, b) aluminium originating from welding of steel objects with the use of a rutile electrode (backscattered electron image, magnification 4000 x).



a) b)

Fig. 3 Iron particles originating from welding of both, aluminium objects and steel objects (backscattered electron image, magnification 4000 x). Thus, a care needs to be taken when evaluating single particles originating from modern ammunition brands primed with non-toxic compounds consisting aluminium or titanium as they may also originate from the electrodes and their coverings that may produce spherical particles containing, e.g. aluminium, titanium, silicon, potassium and chlorine (Fig. 4).

a) b)

Fig. 4 Aluminium particles originating from: a) welding of aluminium objects and b) discharge of Luger 9mm ammunition by Mesko metal Works, Skarzysko-Kamienna, Poland, the year of production 2009 (backscattered electron image, magnification 500-1000x).

2.2 Dependence of the chemical contents of GSR on the type of ammunition

Detection of GSR by means of SEM-EDX can be utilised in establishing the kind of ammunition not only when a cartridge case was found on the crime scene, but also when samples of GSR collected from other substrates, e.g. hands and clothing of the incident participants, are the only accessible evidence for examinations. Both cases demand cautiousness and personal experience of an expert. Results of the examinations on differentiation of GSR originating from various types of ammunition demonstrated the direct co-relation between GSR and the chemical contents of the primer of ammunition and usually in much extend on the chemical content of other parts of the cartridge and so their usefulness in group identification of the type of ammunition [14 -19]. In the case of ammunition of the chemical content different from that of the traditional one, based on the compounds of lead, antimony and barium, the formal classification scheme unfairly lowers the evidential value of some particles and so, it should not be used without criticism. A qualitative comparison of the elemental contents of gunshot residue (GSR) taken from the suspect’s hands with these originating from the cartridge case found at a crime scene seem to be a routine protocol. In the case of agreement it may support the findings concerning the relation of an individual to a shooting as well as provide a clue on the type and calibre of weapon and ammunition used. However, the results of comparison may be misleading if one expects only similar chemical contents of the particles taken from the two substrates. A comparative study was performed for GSR samples taken from the shooter’s hands and from inside the cartridge case, which were obtained using three brands of Luger 9 mm ammunition with primer mixtures based on different types of detonators: mercury fulminate, lead styphnate or lead azide and an organic one, e.g. diazo-dinitrophenol [20]. Two types of lead-free ammunition cartridges with copper and tin plated projectiles were used. Similarities as well as significant differences in the chemical composition and morphology of particles secured from hands of the shooting person and from the appropriate cartridge case were observed. It has been found that the chemical composition of particles originating from the primer may be influenced by the chemical composition of other parts of the cartridge case, especially the core and the jacket of the projectile. The distribution of the chemical elements in gunshot residue strongly depends on the direction of the reaction path starting in the primer cup placed at the bottom of the cartridge case, moving along the cartridge case and the barrel, and finishing when the projectile leaves the gun muzzle. Thus, a reliable comparison of the airborne residue to these



taken from cartridge case for forensic purposes requires some experience based on laboratory experiments performed under controlled conditions.

2.3 Dispersion of GSR

It has been found that SEM-EDX method being normally used for detection of characteristic GSR can also be applied to obtain information on possible differences in sizes of the particles as well as the proportions of their chemical classes depending on the distance from the muzzle of a gun, both in the direction of shooting and the opposite one. A systematic study of various features of GSR collected from targets in the dependence on the shooting distance as well as from hands and the forearm, front and back parts of the upper clothing of the shooting person were performed with SEM-EDX. GSR samples were obtained using Walther P-99 pistol and Luger 9mm ammunition as well as P-63 and P-83 pistols and Makarov ammunition of Polish production [21, 22]. It has been found that in addition to the dependence on the distance from the muzzle the properties of particles are related to the kind of substrate they were collected from, the chemical composition and details of construction of the ammunition, such as the calibre, the load of propellant etc. The mechanisms of formation and dispersion of GSR, despite its being dynamic and complex, proved to be repeatable features of discharge of a certain type of a cartridge. That gives rise to understanding more general rules of the complex process of shooting, e.g. that differences in properties of GSR collected from various substrates and locations in the shooting scene are natural consequence of subsequent interactions of the explosive mixtures with materials constituting each part of the cartridge case and the parts of weapon that are directly related to the internal ballistics. Thus, in some favourable circumstances, when a gun of interest and a load of ammunition are accessible to a forensic expert, the presented novel way of inspection into the features of the examined GSR may contribute to crime reconstruction, especially to establishing the mutual positions and possibly the roles of the persons taking part in the shooting incident. A growing interest towards understanding the mechanism of GSR dissipation in the vicinity of the shooting gun was recently demonstrated also by physical studies of the residue plum originating from various types of firearms and photographed by a high-speed camera [23].

3. Textile fibres

Fragments of single textile fibres are a forensic evidence of a great importance if they could come from the victim's or suspect's clothing. Fibres transferred from an assailant's clothing to that of a victim, and vice versa, as well as fibres present on a victim's body, e.g. under the fingernails, are most often required in order to establish whether or not physical contact took place between individuals, as in cases of murder, sexual abuse, fights, etc. The driver's and passengers' seats, as well as other elements of the vehicle's interior, are also checked for fibre evidence for determining who may have been driving a vehicle during a road accident. Fragments of the single fibres from victims' clothes are frequently found on the knives, scissors, axes used by a perpetrator. Evidence in the form of fragments of a textile fibre is usually not more than a few millimetres in length, and 20 – 25 µm in diameter. It has been the subject of intense scientific studies since the 1970's [24, 25]. Forensic examination of single fibres leads to establishing their characteristic features as colour, shape, surface characteristics, thickness, crystallinity, fluorescent qualities, chemical composition, and on that basis to their identification, classification, comparison with other fibre coming from the known source. For this purpose microscopic methods such as e.g. stereomicroscopy, polarized light, comparison, fluorescence, interference, scanning electron microscopy, and microanalytical methods as microspectrophotometry in the UV and visible range, micro-FTIR spectroscopy, micro-Raman spectroscopy are routinely used [25, 26]. In the course of the production process, a single fibre generally doesn't acquire any individual features, characteristic enough to allow for the identification of a specific fibre product; all that can be established is that it may have come from a set of similar products (known as forensic group identification).

3.1 Damage to fibre

The examination, identification and interpretation of the fibre damage allow drawing more objective inferences about the circumstances of an event and its participants, because in the course of damage textiles acquire unique, characteristics features. In forensic casework, experts deal mainly with mechanical damage to textiles (especially cutting by sharp-edged objects), with the influence of high temperature (and pressure), and of microorganisms (bacteria, fungi) [27, 28]. The examination of the influence of particular damaging factors on the colour and structure of textile fibres are currently the subject of numerous analyses and investigations. Selected results of own studies (by JWG) carried out for different damages to textiles, especially to their constituent fibres, are presented below.

3.1.1 Mechanical damage

By analyzing the textiles, it is often a difficult task for the forensic expert to distinguish between the effects of routine wearing and other kinds of mechanical damage, which may be related to the crime. Damage resulting from routine use



of textiles frequently takes the form of a thinning of the fabric prior to a hole forming, pilling, or even weak tearing. In a violent crime, textiles may be torn intensively, may be cut (with e.g. a knife, a scalpel, a razor blade, scissors), may also be punctured by other a relatively sharp (e.g. a screwdriver) or blunt (e.g. a hammer) object, and the nature of this damage will depend on the textile material itself and supporting material beneath the textiles. There are a large number of variables associated with textile manufacture, including fibre type, yarn structure, fabric/knitting/unwoven construction, applied finishes, fabric orientation, but also with the garment construction and fit, that make examination of this kind of damage a very complex. Generally, the observation of fibre end morphologies should be estimated when analysing mechanical damage to textiles, especially with the use of a higher magnification as in different electron microscopy techniques, and can give a piece of information about a blade type of the cutting object. Theoretically, a sharp blade will cut fibres (and yarns) with little or no distortion; in contrast, a blunt blade increases the disorder of fibre ends and individual fibres fail under tension rather than cutting. Indeed, characteristic features of damaged fibre ends depending on the fibre type and morphology, and in each forensic case it is recommended carrying out simulation experiment on a particular type of textiles and yarns. Fig. 5 summarizes the SEM images of fibres ends from the polyester yarn, obtained in the results of the simulation experiment in the specific forensic case, in which the task of the expert was proposing tool that was used by the offender to the evidential thread intersection.

a) b)

c) d)

Fig. 5 Polyester fibres endings after: a) scissors cutting, b) cutting with the use of blunt (used) knife, c) cutting with the use of a sharp (new) scalpel and d) tensile failure (secondary electron image, magnification 2000 x). During the examination it was found that, in the case of this particular polyester yarn scissor cuts created pinched, rather symmetric ends, with lateral distortion (Fig. 5a); blunt knife cuts produced jagged flat tops (Fig. 5b), sharp scalpel cuts leaved smooth and almost mapped metal surface of the blade of the scalpel, more or less inclined surface of the intersection (Fig. 5c), and in the case of the tensile failure a bulbous top was observed (Fig. 5d).

3.1.2 Thermal damage

The effects of high temperatures seen on the textiles and its fibres are mainly connected with the cases of arson, fire-raising, explosions, firearms or road accidents. In these forensic cases the expert is most often asked to determine the physicochemical change of the fibres after thermal transformation, and this kind of information is useful in establishing the circumstances of the event, and to link a person with it. This is a difficult task without conducting simulation experiments in order to define the characteristic features of damage of this special kind of textiles and fibres. The study in the field of thermally damaged textiles and fibres carried out in cooperation with the Forensic Science Institute, Landeskriminalamt Baden-Württemberg in Germany [29-31] provides investigators with important information on how to link a given textile to specific circumstances of a crime. The typical transformations that occur in textiles and fibres subjected to various degradation factors, as direct exposure to a vapour cloud explosion (VCE), to a heating place at high temperature, and to an open flame have been studied in details, with the use of optical and scanning electron microscopy.



a) b)

Fig. 6 Two types of synthetic fibres: acrylics (a) and polyamides 6 (b) degraded by high temperature of VCE shock wave (a) and of a flame (b) (secondary electron image, magnification 300 x). As an example typical transformations of acrylic fibres being in the area of the vapour cloud explosion (Fig. 6a), and polyamides 6 fibres following contact with the flame of a gas burner (Fig. 6b) have been illustrated. In the case of acrylic fibres (Fig. 6a) the formation of conglomerations on the fibre ends characteristic for very short-term and superficial action of thermal factor was observed. This phenomenon does not appear in damage caused by an open flame e.g. of the polyamide fibres (Fig. 6b), where the observed changes are located on the entire length of the fibres.

3.1.3 Microbiological damage

Microorganisms and fungi can feed on natural fibres, and on many types of textile and fibre additives based on natural substances (for example dyes, spinning oils and softeners), while synthetic fibres are more resistant. Microbiological damage is often seen in cases of textiles coming from exhumations, and is subjected to analysis in order to determine the circumstances of the events of the past [3]. As usual in forensic examination, there is a need to carry out simulation experiment using the same kind of textiles, but it is much more complicated than in the case of the two previous types of damage. Determination of changes in the morphological structure of woolen fabric and fibres of military uniforms, after burial in biologically active soil for a particular period of time was the aim of one of the conducted experiments [32]. The fungal and bacterial attacks led to changes in the colour of the fabric, its looseness and in the morphological structure of the woollen fibres.

a) b)

Fig. 7 The original wool fibres from the fabric of soldiers uniform (a) and fibres from the same fabric after 3 weeks of burring in the biologically active soil (b) (secondary electron image, magnification 1000 x). The deformation of the scales on the surface of wool fibres, which shredded, merged and formed an almost undivided whole, together with a degradation of over half of the fibres was observed [Fig. 7]. The observed changes in the morphological structure of woollen fibres depended mainly on the duration of their burial in the soil, but fibres situated on the external part of the thread were more quickly attacked by the microorganisms than fibres located inside the tread. The final decay i.e. the decomposition of the structure of the fabric of soldiers’ uniforms took place 5-6 weeks after they had been buried in standardized, bioactive soil (literally, nothing was left of the textiles ). Taking into consideration the fact of the varying intensity of the process of biodegradation of particular fibres in the thread, the interpretation of the time of fabric decay based only on a microscopic examination of damaged fibres may be subjected to an error.

3.2 Microspectroscopic methods

Only non-destructive and very sensitive microanalytical techniques may be applied for the examination of forensic microtraces, especially the fragments of the single fibres. From the spectroscopic methods, which are used to examine different aspects of the molecular structure of the fibre itself and its additives introduced during diverse production processes, microspectrophotometry in the visible and UV range, and FTIR microspectroscopy play an essential role.



Nowadays, Raman microspectroscopy proved to be a promising technique in the area of forensic examination of fibres and its colorants (dyes, pigments), especially in order to distinguish between each other. The first one from the mentioned above techniques is a combination of the UV/Vis spectrometer with a transmitted light microscope, being the centre of the system and allowing reproducible focusing of the light on a small fragment of the fibre sample. The absorption or reflectance in the UV/visible range directly affects the perceived color of the dyed fibre. Infrared and Raman spectroscopy measure the vibrational energies of molecules basing on different selection rules. To be active in the infrared, the dipole moment of the molecule must change, while for a transition to be Raman active there must be a change in polarisability of the molecule. Thus, both techniques - Raman and infrared spectroscopy can provide complementary information on the components present in the examined material, e.g. fibres and they molecular and supermolecular structure. FTIR and Raman microspectroscopy enables to collect data from a very small fragment of the single fibres, through a combination of classical spectrometers with optical microscopes. In the last 3 years different kinds of fibres were examined by one of the authors (JWG) using Raman microspectroscopy, with the aim of identification of polymers, dyes, finishing agents as well as crystal structures e.g. cellulose in natural plant and artificial cellulose fibres [33-37]. A method of the appropriate sample preparation for analysis by Raman microspectroscopy was worked out and optimum measurement conditions for a given type of fibre were established. Raman spectroscopy has been found a very useful method for non-destructive comparisons of forensic evidence in the form of single fibers, and the application of many excitation laser wavelengths enables one to identify more specifically bands of the fibre polymer, dyes, additives, and the crystal lattice. A complete and up-to-date database of Raman spectra of dyes and their mixtures is not available on the market, because of the mass production of fibrous material, but our own database of the examined fibres has been created in the Institute of the Forensic Research, Krakow. Although a great work is still required, it is expected that Raman spectroscopy will became a routine method of fibre examinations.

4. Casework application

As mentioned previously the discussed studies of GSR and fragments of the single fibres are applicable in the daily casework in majority of the forensic laboratories. Below there is presented an example of the research of these two types of traces in one case.

4.1 Case description

A man, deadly wounded in the lower part of abdomen, was found by his family in a garage. An electric hot plate, switched on, and a number of cartridges of hunter’s ammunition were present on a desk. No firearm was found in the domestic premises. The autopsy revealed two wounds with channels boring through the skin and intestines. The course of the wound channels were approximately perpendicular to the surface of the body suggesting the horizontal damaging action against the man remaining in the upright position. From the dead ends of the wound channels there were removed elements of a cartridge: a projectile and a deformed cartridge case. Whereas the presence of a projectile inside the soft tissues of the man suggested a gunshot, the deformed cartridge case indicated an explosion of a cartridge. Thus, the outer clothing of the man, i.e. his sweater was sent by the prosecutor for physical and chemical examinations to the Institute of Forensic Research, Krakow for establishing the most probable course of the incident.

4.2 Materials and methods

Within the forensic expertise a sweater of the victim was the subject of the performed physical and chemical examinations. Initially, a visual examination of the probes was performed using a stereomicroscope MZ16 (Leica, Heerbrugg, Switzerland). A detailed morphological study of selected single fibres as well as a search for GSR was performed using a scanning electron microscope JSM-5800 (Jeol Ltd., Tokyo, Japan) coupled with an energy dispersive X-ray spectrometer Inca Energy (Oxford Instruments Ltd., High Wycombe, UK; Si(Li) detector, ATW - atmospheric thin window, resolution 133 eV for MnKα at 10 000 counts). Samples of microtraces from the surroundings of damages in the sweater were collected using aluminium stubs with conductive carbon adhesive tabs by TAAB Laboratories Equipment Ltd., Great Britain. of the upper clothing and the vicinity of the belt and pockets of trousers. About 100 dubbings were made with each stub. Stubs with the collected microtraces were covered with a conductive layer of carbon using a SCD 050 sputter, BAL-TECH, Lichtenstein to avoid charging. The identification of GSR was performed in an automatic manner with an Inca Feature/GSR programme, Oxford Instruments Ltd. The programme automatically searches for particles of defined features, subsequently analysing rectangular frames, into which the whole area of a stub is divided; the number and size of frames depends on the applied magnification and scanning resolution. The initial setting of the program embraces defining the positions of the stubs as well as the Co-Rh standard to establish the range of the back-scattered electron signal, the expected chemical classes of the particles and the limits of particle size. The chemical classes of particles are defined by setting the list of



contributing elements within broad ranges of their composition, typically between 0 and 100%. The measurement setting was selected so that particles of 0.9 μm in diameter would not be missed (Table 1).

Table 1 Analytical parameters of the automatic search for GSR by means of Inca Feature/GSR, Oxford Instruments Ltd.

Magnification 160 x Accelerating voltage 20 kV Working distance 10 mm Minimum size of the particle 0.863 μm Area of the scanned frame 0.537 mm2 Image resolution 2048 x 1408 pixels

4.3 Optical examination of the evidence material

The evidential sweater was black and grey in colour, produced from woollen knitted fabric, with an informational label: „100% Shetland wool”. Two mechanical damages in a form of holes were revealed in the lower part of the front of the sweater:one placed within the ribbing and the other one above the first one. Both holes displayed irregular edges and sizes about 1.5 – 2 cm. In the area of the damages, especially on the reverse side of the sweater, there was also observed a blotting, brown in colour, confirmed later by the hemogenetic examination as a human blood. At the edges of the holes and in their nearest surroundings grains of appearance of an unburned propellant were not revealed by means of optical methods. However, the endings of some fibres within the edges of both holes bore traces of an action of a high temperature, besides a mechanical factor (Fig. 8a). Moreover, above the mechanical damages in the form of holes an extra area of about 2 x 4 cm with thermal changes of the most exterior fibres in the knitted fabric was revealed (Fig. 8b). A sample of microtraces was collected from the surroundings of the holes, excluding their edges, for further examinations towards metallic particles.

a) b)

Fig. 8 Steromicroscopic images of fibres endings of the edge of one of the holes (a) and of thermally damaged surface (b) of the examined sweater (magnification 50-70x).

4.4 Morphological and chemical examinations of selected microtraces

The fragments of fibre endings selected under the stereomicroscope from the surrounding area of mechanical damages of sweater were examined by means of SEM at various magnifications (Fig. 9). Extensive degradation of the woollen fibres was observed; their ends form mainly a bulbous structure (Fig. 9a). The results of gasses escaping (mainly ammonia, hydrogen sulphide) in the process of the wool’s degradation under the high temperature were observed throughout the length of the fibres (Fig. 9b). Wool fibres are generally not very resistant for the high temperature, similarly to all of the protein substances, that undergone the process of denaturation just at temperatures above 100°C. The observed transformations of the wool fibres and especially their ends were typical for thermal factor, which acted on the textile product mostly superficially and relatively shortly.



a) b)

Fig. 9 Fragments of thermally changed woolen fibres collected from the damaged areas of the evidential sweater (secondary electron images, magnification 500x). Among the microtraces collected from the vicinity of the holes in the sweater multiple metallic particles, mainly spherical in shape and containing lead, antimony and barium with a donation of tin and aluminium, were revealed. Numbers of the particles within particular chemical classes are listed in Table 2, and the examples of their morphology presented in Fig. 10.

Table 2 Numbers of particles of particular chemical classes detected in the sample taken from the surroundings of the holes in the sweater.

Chemical classes of particles Number of particles Pb-Sb-Ba (Sn, Al) 6

Sb-Ba (Sn, Al) 11 Pb-Ba (Sn, Al) 53 Pb-Sb (Sn, Al) 20

Sb (Sn) 7 Pb (Sn) over 100 Ba (Al) 2

a) b)

Fig. 10 SEM images of GSR particles detected in the vicinity of the holes in the sweater (backscattered electron images, magnification 5000-6000x).

According to the classification scheme worked out in late seventies of the last century three-component particles containing lead, antimony and barium are unique primer residues. Accompanying two- and one-component particles are indicative for gunshot, since particles of similar elemental contents could have originated from other sources. The presence of primer residues themselves on the body and clothing of a person indicates one of the following possible situations: the person was shooting or handling an object contaminated with GSR, or else present in the nearest vicinity of a detonating ammunition primer.

4.5 Conclusions

The physical and chemical expertise is a complementary item to other sources of information, the final interpretation of the obtained results should be carried out taking into account the circumstances of the incident under consideration [38-39]. While evaluating the forensic findings in the presented case the following evidence and facts were taken into account: the lack of a firearm and no evidence of a break-in to the domestic premises, the presence of deformed and partially fragmented cartridge case in the wound channel of the victim, functioning electric hot plate, and the results of the forensic examinations, i.e. the presence of superficial thermal changes of fibres of the woollen sweater of the victim as well as a relatively great amount of the primer residue.



Thus, one can conclude that the man’s death was most probably self-inflicted by heating an ammunition cartridge and resulting subsequent explosions of its primer and propellant load.

Acknowledgements The study was partially supported by the Polish Ministry of Science and Higher Education (Narodowe Centrum Badan i Rozwoju) within the projects no. 0758/B/T00/2009/36, and 1150/B/T00/2009/36, 2019-2012.

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microscopic and microanalytical examinations of metallic particles

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