Fingerprinting spent shell casings now possible with electrochemical process

The game of Clue (Cluedo in the UK) grows ever more redundant, as improvements in forensics technology make it easier to determine who shot who in the observatory. Witness a new electrochemical test that can recover fingerprints from fired ammunition, even after extreme heat exposure.

A report from SciTechDaily says the method developed by two Irish scientists accomplishes what was long believed to be nearly impossible. The high heat, friction and gasses produced when ammunition is discharged tends to wipe away most biometric traces on a brass casing. That fact has made used bullet casings useless as a way to link a suspect to a crime scene in forensic investigations.

Not anymore.

“The Holy Grail in forensic investigation has always been retrieving prints from fired ammunition casings,” says Dempsey. “Traditionally, the intense heat of firing destroys any biological residue. However, our technique has been able to reveal fingerprint ridges that would otherwise remain imperceptible.”

The technique involves coating casings in an electrochemical solution containing specific polymers. Using a compact device called a potentiostat, a small amount of voltage is applied to the solution, which draws certain chemicals on the casing to the surface, “depositing material between the fingerprint ridges and forming a sharp, high-contrast image.” The process takes seconds.

“Using the burnt material that remains on the surface of the casing as a stencil, we can deposit specific materials in between the gaps, allowing for the visualization,” says McKeever, who compares the process to turning a casing into an electrode.

In technical terms from the paper, the research examines “the spatially selective deposition of conducting/redox active polymers for visualising latent finger-marks on typically low-yield brass ammunition casings, exploiting the electrodeposition of 3,4-ethylenedioxythiophene (EDOT), together with a first-time study of phenozine vs. phenothiazine monomers, and their combinations at sheet and cartridge brass.”

Bullet fingerprinting could leave killers red-handed

The hope is that the technique could provide a more direct biometric link between shooter and victim.

“Currently, the best case of forensic analysis of ammunition casings is to match it to the gun that fired it,” says Dr. McKeever. “But we hope a method like this could match it back to the actual person who loaded the gun.”

Tests, which focused on common brass casings, showed the biometric technique effective on samples as old as 16 months. The researchers think it could be adapted for other metals, expanding its range of potential forensic applications.

Their findings are published in the paper, “Electrodeposition of redox materials with potential for enhanced visualisation of latent finger-marks on brass substrates and ammunition casings,” in Forensic Chemistry.

Article Topics

biometric identification  |  criminal ID  |  fingerprint biometrics  |  fingerprint recognition  |  forensics