Semi-automatic detection of gunshot residue (GSR) by scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDX).

Wide strips of adhesive tape (40 mm x 86 mm) are pressed for about one minute on the thumb, forefinger and outer edge of a subject's hand. Subsequently these tapes are fixed to a cylinder that rotates within the SEM chamber and is adjustable in an axial direction. The tapes are scanned for possible GSR particles with simultaneous SE and X-ray imaging. The X-ray signal caused by particles of high atomic number automatically stops the rotating cylinder, and the EDX spectrum of the suspect particle is produced within five seconds. A chart is then plotted to record the size, elemental composition, morphology and tape coordinates of the particles of interest. The outcome is a complete map of GSR particles found on certain parts of the hand, and this map has a characteristic pattern depending on the firearm used, the ammunition and the circumstances of the shooting incident. The time lapse between firing and sampling may allow this GSR pattern to change, but this method is helpful in suicide/homicide decisions.