The presence of gunshot residues on a suspect or suspect’s clothing can tie that suspect to the crime scene. An important forensic application of ultramicroanalysis at McCrone Associates is the searching for gunshot residues by scanning electron microscopy (SEM). Today, very few independent laboratories have the expertise, experience and instrumentation to conduct these extremely important forensic tests.
Gunshot residues originating from the primers in most cartridges are usually spherical particles, often very small (<5 micrometers), and contain antimony, barium and lead. They are characteristic particles and extremely valuable evidence to show that a person recently fired a gun, was in close proximity to a gun when fired or came into contact with an object that had gunshot residue on the surface.
Samples can be collected directly from the hands and clothing of the suspect onto specially coated SEM stubs. The stubs are then placed in the SEM and/or electron microprobe analysis to search for and identify these characteristic particles of antimony/barium/lead that indicate gunshot residue.
Essentials of Polarized Light Microscopy and Ancillary Techniques by John Gustav Delly has been published.
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