Overview: A New Fingerprint Recovery Technique for Brass Casings
Researchers at Maynooth University have developed an electrochemical method that can visualize fingerprint ridges on brass bullet casings after they are fired. This breakthrough challenges the long-held assumption that the intense heat and gas released during firing obliterate biological traces, such as fingerprints, on ammunition. Led by Dr Eithne Dempsey and PhD student Dr Colm McKeever from the Department of Chemistry, the team asserts that a thin layer of specially chosen materials can make hidden prints visible once more, offering a potential new tool for criminal investigations.
The Scientific Breakthrough
Traditional fingerprint detection on spent casings faces the problem that heat and friction typically destroy residues. The Maynooth approach instead coats brass casings with a thin polymer layer and places the item in an electrochemical cell. By applying a controlled voltage to the casing acting as an electrode, the chemistry at the surface is driven in such a way that the spaces between fingerprint ridges become coated with chemical substances. The result is a high-contrast image of the print, revealing ridges that otherwise would be imperceptible to investigators.
How the Method Works
The team describes a process that uses a potentiostat to regulate voltage with remarkable portability—potentially allowing a compact forensic kit to be carried in the field. In practice, the brass casing is immersed in a solution within the electrochemical cell. A small voltage causes the solution’s active components to migrate to the surface, depositing selectively between fingerprint ridges. This creates a clear, legible print image without relying on more hazardous chemicals or bulky equipment typical of some existing techniques.
Why Brass Has Been Historically Challenging
Brass is a common material for ammunition, but its surface chemistry makes latent prints especially difficult to recover after firing. The Maynooth method overcomes this by turning the case itself into part of the electrochemical system, enabling targeted surface reactions that highlight ridge detail rather than attempting to lift prints directly from the exhausted surface.
Potential Applications and Advantages
According to the researchers, the new technique uses readily available, non-toxic polymers and low energy input, reducing safety concerns and operational costs. Beyond firearms, they believe the approach could adapt to other metallic surfaces, widening its forensic reach to arson investigations and other incidents where metal objects might bear traces of human contact.
Validation, Publication, and Next Steps
The study—funded by Research Ireland and Maynooth University—was published in the forensic science journal Forensic Chemistry. The researchers emphasize that, while promising, the technique must undergo rigorous testing and external validation before law enforcement agencies can routinely adopt it. Questions remain about reproducibility across different lab conditions, potential interference from contaminants, and how results are interpreted in real-world crime scenes.
Implications for Forensic Science and Law Enforcement
If validated, recovering fingerprints from fired bullet casings could become a valuable link in crime scene reconstruction, helping identify individuals who handled ammunition in the moments before a crime. As Dr Dempsey notes, the field has long sought a reliable method to retrieve prints from spent casings; this work could mark a meaningful step toward that goal. Yet researchers caution that real-world testing, standardized protocols, and independent verification are essential before the method could support prosecutorial processes.
About the Researchers and Funding
Dr Eithne Dempsey and Dr Colm McKeever led the research team at Maynooth University, with support from Research Ireland. The collaboration reflects a broader push to leverage electrochemistry and polymer science for practical forensic tools that are safe, scalable, and portable for modern investigative work.
