Now, a New Scientist investigation has found that someone who has never fired a gun could be contaminated by someone who has, and that different criminal investigators use contradictory standards. What's more, particles that are supposedly unique to GSR can be produced in other ways.
Forensic scientists often testify that finding certain particle types means the suspect handled or fired a weapon. Janine Arvizu, an independent lab auditor based in New Mexico, reviewed the Baltimore county police department's procedures relating to GSR. Her report concludes: "The BCPD lab routinely reported that gunshot residue collected from a subject's hands 'most probably' arose from proximity to a discharging firearm, despite the fact that comparable levels of gunshot residue were detected in the laboratory's contamination studies." The BCPD did not return calls requesting comment.
Some specialists argue for a more cautious approach. "None of what we do can establish if anybody discharged a firearm," says Ronald Singer, former president of the American Academy of Forensic Sciences and chief criminalist at the Tarrant county medical examiner's office in Fort Worth, Texas.
Peter De Forest of John Jay College of Criminal Justice in New York goes further. "I don't think it's a very valuable technique to begin with. It's great chemistry. It's great microscopy. The question is, how did [the particle] get there?"
GSR analysis is commonly
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23-Nov-2005