Thinking beyond the lab: organic gunshot residues in an investigative perspective

Gunshot residues (GSR) are a common form of evidence in cases involving questions related to the association of a person of interest (POI) to a firearm-related event. GSR analyses currently focus on the detection and characterisation of the inorganic components of GSR (IGSR), which are typically particles composed of lead, barium and antimony originating from the primer. However, certain particles cannot be assigned to IGSR with a high degree of confidence due to possibility of being derived from industrial or domestic sources. Moreover, the increasing prevalence of the use of heavy metal-free ammunition challenges the current protocols used for IGSR analysis. In order to provide complementary evidence to IGSR particles, the current study focused on detecting the organic components (OGSR) arising from ammunition propellant. As the study focuses on the persistence of OGSR, three compounds well known as being part of OGSR were selected: ethyl centralite (EC), diphenylamine (DPA) and N-nitrosodiphenylamine (NnDPA). The study assessed the retention of OGSR traces on a person’s hands up to 1 h after they had discharged a firearm.