Wednesday in the Age of Reason-Munchausen (1988)

Secondary transfer is a bugaboo in forensic science. As instrumentation has picked up increasingly microscopic trace evidence, the concern an innocent person could be implicated by DNA or other molecules from a crime scene has become an increasing focus of defense arguments—and of laboratory research.

Organic gunshot residues can be transferred through weapons handling, handshakes and arrests, according to new trials undertaken by a Swiss and Australian team and published in the journal Science and Justice.

“This study highlights that the secondary transfer must be taken into account in the interpretation of organic gunshot residue,” the scientists write. “Indeed, an individual’s hands might be contaminated by handling a firearm or having physical contact with a shooter.”

Previous studies (and guidelines) have assessed the secondary transfer of inorganic residue that comes from a gunshot’s primer, projectile, cartridge or the firearm body itself. The organic residue instead comes from the propellant and lubricant emerging from the gun—and it is less studied.

The team focused on three separate scenarios: the handing of a handgun to a person who didn’t pull the trigger, a handshake between the shooter and a witness, and a mock-arrest scenario involving handcuffing on the ground, according to the study.