Researchers at Maynooth University in Ireland have created a novel electrochemical process to recover fingerprints from fired bullet casings, a breakthrough long considered impossible in forensics. The safe, non-toxic technique reveals hidden ridges on brass casings in seconds using mild voltage. This could allow investigators to link evidence directly to suspects rather than just weapons.
Two scientists from Maynooth University's Department of Chemistry, Dr. Eithne Dempsey and her former PhD student Dr. Colm McKeever, have designed an electrochemical method to visualize fingerprints on brass ammunition casings after they have been fired. For decades, forensic experts have faced challenges in retrieving such prints due to the extreme heat, gas, and friction from gunfire, which typically destroy biological residues. This has allowed criminals to assume that fired casings could not connect them personally to crime scenes.
"The Holy Grail in forensic investigation has always been retrieving prints from fired ammunition casings," said Dr. 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 process involves placing a brass casing in an electrochemical cell with a chemical solution. A low electrical voltage is applied, drawing chemicals to the surface to fill gaps between fingerprint ridges, using the burnt residue as a stencil for high-contrast imaging. It employs environmentally friendly polymers and requires minimal energy, without toxic chemicals or expensive equipment. Tests confirmed effectiveness on casings aged up to 16 months.
"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 visualisation," said Dr. McKeever. The method turns the casing into an electrode, controlled by a portable potentiostat similar in size to a mobile phone.
Currently, forensic analysis of casings mainly matches them to the firing gun. "But we hope a method like this could match it back to the actual person who loaded the gun," Dr. McKeever added. Focused on common brass casings, the technique shows potential for adaptation to other metals in crimes like arson. Supported by Research Ireland and Maynooth University, the work was published in Forensic Chemistry in 2025.