A subsequent procedure for further deciphering weapons after application of the Trace Metal Detection Test (TMDT): Proof of concept

Abstract

The trace metal detection test (TMDT) is an effective and convenient technique to potentially link perpetrators and metallic weapons by comparing morphological information of developed imprints and suspected weapons. However, metallic items without characteristic patterns and incomplete contact with weapons often lead to inadequate morphological features in developed imprints on hands, resulting in difficulty in identifying suspected weapons and a failure to demonstrate potential relationships between perpetrators and weapons. This paper presents a subsequent procedure, after application of the TMDT, for inferring possible weapon-source of a specific imprint. As a proof of concept, all the experiments involved metallic items as an example and were carried out under controlled laboratory conditions. An analytical method was established by selecting elements of interest in developed imprints from seven metallic items (three groups), undertaking quantitative ICP-MS determination of the elements, and comparing the elements in these imprints (inter- and intra-group comparisons) and with those in their source items. Using the established method, possible groups and types of source metallic items could be inferred based on elemental characteristics in imprints, under the premise that no other metal sources exist before or after contacting specified metallic items. This method could be useful for providing investigative clues and evidence of association for developed imprints that lack unique morphological features and for verifying the results of color reactions in the TMDT. For this reason, it can serve as a standard supplementary procedure after the application of the TMDT, which could further strengthen the correlations between perpetrators and weapons even common metallic objects.