Detection of gunshot residues on the hands by trace element analysis.

In the investigation of cases involving shooting, one of the important links in the chain of proof is evidence that a person fired the gun or was in some way connected with the firing. This has long been attempted by the detection of gunshot residues on the hands of the suspect. One of the early methods was the familiar “paraffin cast” or “dermal nitrate” technique. Warm paraffin was poured on the hands; the paraffin, upon cooling, formed a cast. The cast was then peeled off and the adhering powder residue was detected by means of a color reaction of the nitrate with diphenylamine reagent. Although the paraffin cast was accepted as a method of lifting the residues, the diphenylamine reaction proved to be unsatisfactory in that numerous false positives were encountered. Any substance containing nitrate, such as cigarette ash and urine, gave a positive reaction. The method was therefore abandoned as a means of detecting gunshot residues [1].