Errors in gunshot residue assessment by scanning electron microscopy/ elemental analysis in criminal cases: III. Friction-brake particles assigned as “highly specific” gunshot residue particles

Automated scanning electron microscope analyses of gunshot residue samplers are being performed by many crime laboratories all over the world. Often the criminalist-technician operators of these instruments do not have adequate training for the interpretation of spectra generated by energy dispersive X-ray spectroscopy (parts I and II of this series) and distinguishing gunshot residue from similar composition particles from an environmental source (this article). In this case, gunshot residue-like particles were found on samplers from the hands of the defendant. The criminalist-technician called many of these particles “highly specific of gunshot residue.” The presence of prominent iron with small copper and zinc peaks in almost all these “highly specific of gunshot residue” particle spectra indicate an automotive friction-brake origin. Gunshot residue from the victim and witness (bystander) samplers do not have associated iron, copper and zinc.