Digital infrared photography to develop GSR patterns†

Digital infrared photography can be used by crime scene investigators as a nondestructive test for examining gunshot residue (GSR) on dark and multi-colored fabrics found at the crime scene. When a firearm is discharged a plume of gunshot residue exits the barrel and creates a visible powder pattern on light-colored clothing at specific muzzle-to-target distances. GSR consists of nitrates and nitrites from burned and partially burned smokeless powder and carbon. When GSR patterns are found on dark or multi-colored clothing, the GSR pattern is not readily visible because of the background color of the cloth. A procedure for recording digital infrared images of GSR patterns on dark and multi-colored fabric was developed and tested on 10 samples of dark and multi-colored fabric. A 9 mm pistol was used to produce the GSR patterns on fabric-covered cardboard targets. Digital infrared images were photographed with a 35 mm Nikon D-70 camera using a 67 mm Tiffen® #87 infrared filter. † This paper was presented at the 18th International Symposium on the Forensic Sciences, Fremantle, Western Australia, April 2006.