Advancing the use of LIBS mobile technology in shooting reconstructions and firearm-related investigations

Microscopic residues transferred between surfaces during a shooting event are crucial for crime scene reconstruction. Identifying this evidence on-site is ideal, as overlooked items can be lost or become unreliable. This proof-of-concept study demonstrates that mobile Laser-Induced Breakdown Spectroscopy (LIBS) technology offers innovative capabilities for in-situ enhanced imaging, rapid single-particle analysis, and sensitive multi-elemental detection. LIBS is evaluated for characterizing trace residues from the shooter's hands, impacted surfaces, and other firearm-related components. Eight substrates commonly found at shooting scenes (drywall, painted drywall, architectural sheet glass, plywood, concrete, and vehicle windshield, fender, and side door) are fired at using three types of bullets (full-metal jacket, jacketed hollow point, and lead round nose), resulting in either perforation or ricochet. The transferred residues are identified by their microscopic morphology and emission spectra. Approximately 2100 spectral comparisons with control samples reveal multiple instances of transfer of gunshot residue (GSR) and substrate residues (e.g., drywall, concrete, and automotive parts) onto the shooter's hands across all experiments. Detection rates in replicate experiments varied from 33 % to 100 %, depending on the bullet type, trajectory interactions, and substrate properties. GSR was detected in 95 % of samples collected from the shooter's hands and bullet entry holes. The transfer or residues from seven of the eight substrates (87.5 %) to recovered bullets is demonstrated. The transfers of metal shavings from the bullet or cartridge case to the shooter's hands and bullet hole are observed, varying by bullet type. The evidence of multiple residue transfers from GSR, bullets, and substrates onto a shooter's hand, as well as cross-transfers between bullet and substrate surfaces, and the ability to detect them using rapid, reliable technology can substantially enhance the investigative and probative value of forensic evidence in firearm-related investigations.