Determining the lifetime of detectable amounts of gunshot residue on the hands of a shooter using laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) has been used to determine the period of time that a shooter will test positive for gunshot residue (GSR) after firing a revolver. Multiple rounds of primer were fired and samples collected at multiple hour intervals using an adhesive tape pressed against the skin. Samples were analyzed directly using a commercially available laser-induced breakdown spectrometer where barium emission (originating from barium nitrate in the primer) was observed. Population statistics were used to compare suspected GSR to a library of blank samples from which a threshold value was established. Statistically significant results, positive for GSR, are obtained 5.27 days after a firearm discharge using these techniques.

Laser-Induced Breakdown Spectroscopy for the Rapid Characterization of Lead-Free Gunshot Residues.

This study investigated the use of laser-induced breakdown spectroscopy (LIBS) and scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) as means of characterizing gunshot residue (GSR) originating from commercially available lead-free rounds. Data from two experiments are presented in this work. One experiment focused on identifying prominent analytical markers present in lead-free GSR by LIBS while the other applied SEM-EDX to determine the degree of evidence preservation after LIBS analysis. Samples of GSR were collected via tape-lift method from the hands of volunteer shooters and instrumental analyses were conducted in triplicate. As a result, the lead-free ammunition analyzed in this work generated GSRs comprising primarily Ba, Al, Si, and/or K. Trace amounts of Ti, Fe, and S were also apparent in some compositions. Through SEM-EDX analysis, a spheroidal geometry consistent with traditional lead-containing GSR was observed. Additionally, it was determined that evidence is preserved after LIBS analysis which supports the implementation of LIBS as a rapid preliminary screening method followed by confirmatory testing via SEM-EDX on the preserved evidence.