Firearm contamination

The NAA method for the determination of firearm discharge residue has been generally accepted, but applications have been limited to just a few laboratories. In the process of establishing NAA capability for the State of Illinois crime laboratories we re-examined the standard techniques (10). In the course of our work it became clear that post-irradiation is the cause of several constraints which have discouraged a more widespread use of NAA. The inherent time limitation due to the 87 min. half-life of 139Ba necessitates fast manipulations of radioactive solutions which in turn requires an experienced radiochemist. In addition to an ever present danger of overexposure and contamination, typically only a dozen samples can be irradiated per batch, which makes the method quite expensive. The developed statistical bivariate-normal analysis (11) is convenient for routine applications. With this in mind, a method was developed which a) eliminates post-irradiation radiochemistry and thus maximizes time for analysis b) accommodates over 130 samples per irradiation capsule (rabbit) c) does not require a collection of occupational handblanks and d) utilizes a simplified statistical concept based on natural antimony and barium levels on hands for the interpretation of data. The detailed procedure will be published elsewhere (15). 

Physical evidence collected at crime scenes is sealed in special containers to prevent contamination and degradation and is catalogued carefully. A chain of custody is established and documented as the evidence is sent to a forensic laboratory. At the laboratory, the evidence is examined by personnel trained in one of several fields Forensic serologists examine body fluids, forensic pathologists examine human remains, firearms technicians classify and test firearms and explosives, and forensic chemists determine the composition and identity of materials. 

With the emphasis on quality all systems were explored, both internal and external, with a view to ensuring that they could withstand close scrutiny from any source, that the possibility of cross contamination of suspects with explosives and/or firearm discharge residue is minimized, and that contamination risks within the laboratory are identified and minimized or eliminated. 

Particles on the outside surface of newly acquired, unopened ammunition were examined in order to determine if the ammunition was contaminated with discharge residue in the factory. Munitions and firearms manufacturers do test-fire their products. Results are given in Table 20.1. 

There is no lead or barium in the primer yet discharge particles from this ammunition frequently contain lead, antimony, and barium. The lead and barium must come from other components in the ammunition (bullet core/propellant) and/or from contamination in the firearm. Tin was also frequently present in the discharge particles and originates from the tinfoil disc used to seal the primer cup in mercury fulminate primers. 

The major problem associated with trace evidence is the possibility of cross transfer to the suspect from some unrelated source. In Northern Ireland there must be a greater contamination risk than in the rest of the United Kingdom, due to the relative abundance of firearms and explosives. Cross-contamination allegations are a frequently used defense in court. Contamination risks have been exaggerated out of all proportion, and all problems in this area stem from the difficulty in providing basic facts, knowledge, and statistics... 

During this time he experienced many complex and controversial cases, the vast majority of which were terrorist-related incidents. His main interests include the chemical examinations relating to firearms casework, research and development work arising from same, crime scene examination, health and safety issues, quality assurance, suspect handling and processing, and contamination avoidance procedures both inside and outside the laboratory. 

Examples of ORM-D materials include low-concentration acids, charcoal lighter, spray paint, disinfectants, and cartridges for small firearms. Even though the container sizes may be small, the products inside can still cause contamination of responders or death and injury if not handled properly. 

Two methods are primarily used to detect hidden explosives, as shown in Figure 21.1 bulk detection, which determines the existence of suspicious objects such as knives, firearms, and explosive devices from their shapes and trace detection, which detects the presence of explosive contaminants by chemical analysis of vapor from objects. 

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