An exploratory study of the potential of LIBS for visualizing gunshot residue patterns

María López-López; César Alvarez-Llamas; Jorge Pisonero; Carmen García-Ruiz; Nerea Bordel

doi:10.1016/j.forsciint.2017.02.012

An exploratory study of the potential of LIBS for visualizing gunshot residue patterns

Forensic Sci Int. 2017 Apr:273:124-131. doi: 10.1016/j.forsciint.2017.02.012. Epub 2017 Feb 21.

Authors

María López-López¹, César Alvarez-Llamas², Jorge Pisonero², Carmen García-Ruiz¹, Nerea Bordel³

Affiliations

¹ Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering & Research Institute of Police Sciences, Edificio Polivalente de Química, University of Alcalá, Ctra. Madrid-Barcelona Km. 33.600, 28871 Alcalá de Henares, Madrid, Spain.
² University of Oviedo, Faculty of Science, Department of Physics, c/Calvo Sotelo s/n, 33006 Oviedo, Spain.
³ University of Oviedo, Faculty of Science, Department of Physics, c/Calvo Sotelo s/n, 33006 Oviedo, Spain. Electronic address: bordel@uniovi.es.

PMID: 28267647
DOI: 10.1016/j.forsciint.2017.02.012

Abstract

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800μm, using a stage displacement velocity of 4mm/s and a laser frequency of 5Hz was employed (e.g. an area of 130×165mm² was measured in less than 3h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258-289 and 446-463nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area.

Keywords: Distance estimation; Forensic analysis; Gunshot residues; Imaging; LIBS.