It would definitely be a very good thing if forensic teams could easily extract fingerprints from bullet casings left at crime scenes, but unfortunately, doing so is often quite difficult. But now, a new technology developed at the University of Nottingham could change that.
Fingerprint compounds such as amino acids and lipids tend to evaporate and/or degrade when the cartridge case is ejected due to its exposure to gunpowder residues, high temperatures and pressures while in the gun. So getting usable fingerprints from what’s left is a challenge, made even more challenging by the fact that cartridge cases are cylindrical – if they’re flat, extracting undeformed fingerprints from them will much easier.
To address these issues, the Nottingham team, led by Dr James Sharp, investigated an existing technique called time-of-flight secondary ion mass spectrometry, or ToF-SIMS for short.
It involves focusing high-energy beams of positive ions onto a surface—like the outside of an outer shell—where they release secondary ions that collide with them. Using a device called a time-of-flight analyzer, these secondary ions are then separated from each other according to their mass-to-charge ratios to produce a spectrum that indicates the chemical composition of the sample.
During the process, the cartridge case rotates slowly on a custom-designed platform, so its cylindrical shape is not an issue.
In tests on the casings of bullets fired from the Webley Mk II revolver, the technology was able to reveal details such as fingerprint ridges and sweat holes – which are not available with the usual cyanoacrylate fumigation technique. And importantly, the ToF-SIMS method does not harm the fingerprints, leaving them intact for future analysis.
“This could really pave the way for new and robust ways of analyzing evidence, identifying people of interest and linking them to ammunition in firearms,” Sharp said.
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