A new electrochemical process allows forensic investigators to visualize fingerprints on spent brass ammunition casings, a breakthrough that could help solve crimes by linking individuals to fired bullets. For decades, this has been considered a nearly impossible task in forensics, as the intense heat, pressure, and friction generated during firing typically obliterate any biological evidence left on the shell. This new method, developed by researchers in Ireland, offers a potential solution that is both effective and efficient, creating high-contrast images of prints that were previously thought to be lost forever.
The challenge of lifting prints from shell casings has long been a major obstacle in criminal investigations. When a gun is fired, the casing is subjected to temperatures high enough to vaporize the oils and sweat that constitute a fingerprint. Any remaining residue is often degraded, and the force of the ejection from the firearm can further damage the print. This has meant that casings left at crime scenes, while useful for ballistic matching to a specific firearm, could rarely be used to identify the person who handled the ammunition. Confident that this evidence is destroyed, criminals often leave casings behind. While some methods have been attempted in the past, their success rates have been extremely low, leading many forensic labs to abandon the practice of trying to recover prints from spent cartridges.
A Novel Electrochemical Approach
The new technique, developed by researchers at Maynooth University’s Department of Chemistry, circumvents the issues of heat and friction by detecting the microscopic residue that remains embedded on the casing’s surface. The method works by treating the natural oils and sweat left by a finger as an insulating stencil on the conductive brass casing. The invisible print acts as a mask, blocking a chemical reaction on the metal where the skin’s residue is present.
To reveal the print, the brass casing is placed into an electrochemical cell filled with a solution containing specialized, non-toxic polymer chemicals. A very small electrical voltage is then applied to the casing for a short period—one study noted a current of approximately 0.1 volts for 120 seconds. This causes the polymers in the solution to adhere to the brass surface, but only in the spaces between the fingerprint ridges where the metal is exposed. This process of deposition creates a negative image of the print, making the once-invisible ridges and patterns clearly visible with high contrast.
The Research and Its Results
Development at Maynooth University
The pioneering work was led by Dr. Eithne Dempsey and her Ph.D. student, Dr. Colm McKeever. Their findings were published in the peer-reviewed journal Forensic Chemistry, detailing the first reported use of electrochemical phenothiazine co-polymer deposition for fingerprint analysis on brass ammunition. This specific chemical approach proved to be surprisingly effective. The researchers reported that the test was incredibly successful, revealing fine details of the fingerprints, including the individual pores within the papillary ridges, which speaks to the high resolution and accuracy of the method.
Durability and Longevity
One of the significant findings from the research was the durability of the latent prints when subjected to the electrochemical process. The technique demonstrated extraordinary longevity, suggesting that prints could be recovered from casings long after being fired. This durability is crucial for real-world applications, where evidence may not be collected and analyzed immediately. The ability to recover such detailed prints from a surface that has undergone the extreme stress of firing represents what Dr. Dempsey has called the “Holy Grail in forensic investigation.”
Advantages Over Previous Methods
Unlike many traditional forensic techniques, this new electrochemical method avoids the use of harsh or dangerous chemicals. It relies on readily available, non-toxic polymers and consumes a minimal amount of energy, making it a safer and more environmentally friendly option for crime labs. The primary piece of equipment required is a potentiostat, a device that controls the voltage in the electrochemical cell. Modern potentiostats can be as small as a mobile phone, opening the possibility of developing a portable kit for use in the field.
This stands in contrast to other advanced forensic techniques, such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), which has also been explored for analyzing casings. While effective, ToF-SIMS requires large, expensive equipment and is a more complex process involving high-energy ion beams. The simplicity, safety, and portability of the electrochemical method give it a distinct advantage for widespread adoption by law enforcement agencies. It provides a more accessible tool that could be integrated into standard forensic workflows without significant investment in specialized hardware or training.
From Lab to Law Enforcement
Before the technique can be deployed in active criminal cases, it must undergo a rigorous process of testing and validation to meet the stringent standards of forensic science. This involves further studies to determine its reliability across a wide range of conditions, ammunition types, and environmental exposures. Researchers and forensic experts will need to establish standardized protocols for its use to ensure that the evidence it generates is admissible in court. The scientific community will also need to replicate the results to confirm the method’s robustness.
The potential impact on criminal justice is substantial. Ballistic analysis can link a casing to the gun that fired it, but it cannot identify the shooter. This new technique offers the possibility of connecting a casing directly to the individual who loaded the ammunition. As Dr. McKeever stated, “Currently, the best case of forensic analysis of ammunition casings is to match it to the gun that fired it. But we hope a method like this could match it back to the actual person who loaded the gun.” If validated, this tool could provide a crucial new stream of evidence, helping to solve gun-related crimes and identify suspects from the minute traces they leave behind.
