Nano-Forensics ---- Nanoparticles in Gun-Shot-Residue

Analysis of Gun-Shot Residue (GSR) is a very critical step in Forensic studies of shooting and related criminal cases. However, the current techniques used for GSR analysis are not complete. Detailed information regarding the elemental and crystallographic signatures of the GSR are missing. Moreover the analysis requires a substantial amount of sample which is difficult to obtain and frequently might be contaminated. The current study on the GSR focuses on these deficiencies. Electron Microscopic studies of the metallic nanoparticles (10-100 nm in diameter) obtained from GSR at different target distances from a Winchester Super-X 9mm luger has been analyzed in detail. Perfectly spherical (diameter ~ 10 nm) and very crystalline Pb and Sb nanoparticles were observed. Theoretical studies explaining the formation of the nanoparticles is reported. The non-equilibrium thermodynamic processes leading to the synthesis of the nanoparticles was observed to be very similar to the artificial chemical synthesis methods (e. g. CVD, Laser Ablation etc.). A simplified model will be proposed to explain the nanoparticle synthesis process in the GSR. This additional information obtained from the nanoparticle synthesis model will provide valuable forensic evidence in solving criminal cases. Forensic benefits of this information will be discussed. This ingenious synthesis mechanism has been demonstrated in synthesizing pure crystalline form of other popular nanomaterials..