Use of luminescent gunshot residues markers in forensic context-Part II.

Gunshot residues (GSR) are important physical evidence in firearm-related crimes. Recently developed non-toxic ammunition, however, requires a new methodology for its characterization. To overcome this drawback, the introduction of noncommercial luminescent markers in ammunition was proposed. These markers, synthesized and added to the gunpowder, presented as a versatile tool for GSR analysis, since they require UV radiation alone to visualize the luminescent GSR (LGSR). This has opened up new perspectives for understanding GSR behavior at a crime scene. This work aims to expand previous studies performed with the luminescent markers in forensic contexts, exploring four different important aspects related to GSR behavior. Using LGSR amount/dispersion and a series of blind tests with marked ammunition, we tried to (1) identify the shooter position; (2) estimate the shooting distance; (3) evaluate the influence of the pistol type on the LGSR distribution on the shooter's hands and guns; and (4) study the transference of LGSR by a chain of handshaking. For this purpose, a portable UV lamp (λ=254nm) and/or techniques such as video spectral comparator (VSC) and scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS) were used to visualize and analyze the residues. As a result, the observation of the LGSR enabled accurate determination of the shooter position and the firing distance without any chemicals. Besides, the LGSR were visualized on different kinds of pistols, regardless of firing mechanism. And finally, this study evidenced transference of residues from shaking hands with the shooter, which should be carefully considered when interpreting the results of a GSR analysis.