NCJ Number
19965
Date Published
1974
Length
70 pages
Annotation
DESCRIBES PARTICLE ANALYSIS TECHNIQUES USING THE SCANNING ELECTRON MICROSCOPE TO PROVIDE MORE INFORMATION ABOUT GUNSHOT RESIDUE THAN CONVENTIONAL TECHNIQUES WHICH MEASURE THE CONCENTRATION OF ELEMENTS.
Abstract
THE SCANNING ELECTRON MICROSCOPE WITH ENERGY-DISPERSIVE X-RAY FLORESCENCE DETECTION HAS BEEN USED TO PROVIDE HIGHLY RELIABLE IDENTIFICATION OF GUNSHOT RESIDUE PARTICLES. THE RESIDUE PARTICLES DEPOSITED ON THE HAND WERE EXAMINED FOR MORPHOLOGICAL CHARACTERISTICS AND ELEMENTAL COMPOSITION. THE PARTICLES CAN BE CLASSIFIED INTO THREE CATEGORIES: PARTIALLY BURNED FRAGMENTS OF DISTINCTIVE APPEARANCE; PARTICLES OF SPHERICAL OR DISTORTED SHAPE; AND NONDESCRIPT PARTICLES. ALL THREE TYPES CONTAIN COMBINATIONS OF LEAD; BARIUM, AND ANTIMONY. THE COMBINATION OF MORPHOLOGICAL AND ELEMENTAL INFORMATION IS ADEQUATE TO PERMIT RELIABLE IDENTIFICATION OF RESIDUE HANDSAMPLES. A SET OF RANDOMLY MIXED 'UNKNOWN' SPECIMENS WAS FORMED FROM 15 FIRING HANDSAMPLE SPECIMENS AND 16 NON-FIRING HANDSAMPLE SPECIMENS (HANDBLANKS) THAT HAD BEEN COLLECTED RAPIDLY AND EASILY BY PRESSING AN ADHESIVE LAYER ATTACHED TO ALUMINUM BLOCKS AGAINST THE HAND SURFACE. IN A BLIND TEST, THE ANALYST WAS ABLE TO CORRECTLY IDENTIFY EACH ALUMINUM BLOCK, FREQUENTLY WITHIN 10 MIN TIME. SINCE ONE-HALF OF THE FIRING SPECIMENS WERE FROM .22 CALIBER HANDGUN FIRINGS, WHICH ARE DIFFICULT TO DETECT BY OTHER METHODS, AND ONE-HALF OF THE HANDBLANKS WERE FROM INDIVIDUALS WITH HIGH EXPOSURE TO CONTAMINANT PARTICLES, THE 100 PERCENT SUCCESS OF IDENTIFICATION BY USE OF THE SCANNING ELECTRON MICROSCOPE A MAJOR IMPROVEMENT OVER CURRENT METHODS OF RESIDUE DETECTION. (AUTHOR ABSTRACT MODIFIED)