AFTE Store - PROBLEMS ENCOUNTERED IN THE DETECTION OF GUNSHOT RESIDUES

The purpose of this work was to highlight the different problems that may be encountered when a firing distance is evaluated on the basis of gunshot residue (GSR) dispersion on victim’s clothing. Test shots were fired at the same distance using different brands of .38 Special and 9 mm Parabellum ammunition. Gunshot residues were visually compared then chemicaly treated for the presence of nitrites (modified Griess test) and heavy metals (sodium rhodizonate test). The experiments were designed to evaluate the efficiency of these different methods on a variety of textile surfaces (cotton, wool, silk and synthetic). The detection of nitrite residues on woolen clothing presented certain difficulties and it was found that the N,N -diphenylbenzidine test, although toxic and carcinogenic, gave clearly superior results on this type of material. The persistence of GSR on cloth supports subjected to different climatic conditions was also studied. The samples were kept several days in stagnant water (port), running water (river), snow, and humid soil (forest) and the persitence of the firearms residues compared to that for reference samples kept in the laboratory. The effects of blood staining on the evaluation of shooting distance was also investigated. A questionnaire was addressed to all of the police forensic services in Switzerland in order to ascertain the breadth fo GSR-related work conducted by the technicians within each of these services. The results from this survey also constitute part of the present study.