New technique excels at lifting fingerprints from shell casings
It would be great if forensics teams could easily lift fingerprints off of bullet casings left at crime scenes, but unfortunately doing so is often quite difficult. A new technique developed at the University of Nottingham could change that.
Because casings are exposed to gunpowder residue, hot temperatures and high pressure while still in the gun, fingerprint compounds such as amino acids and lipids are often evaporated and/or degraded by the time those casings are ejected. Obtaining a usable print from whatever's left is therefore challenging, made even more so by the fact that the casings are cylindrical – if they were flat, it would be easier to lift non-distorted prints from them.
In an effort to address these problems, a Nottingham team led by Dr. James Sharp looked to an existing technology known as Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS).
It involves focusing high-energy beams of positive ions onto a surface – such as the outside of a shell casing – where they free up secondary ions with which they collide. Utilizing a device known as a time-of-flight analyzer, those secondary ions are then separated from one another according to their mass-to-charge ratio, "producing a spectrum that is indicative of the sample’s chemical composition."
The casing is slowly rotated on a custom-designed platform while this process is being performed, so its cylindrical shape is not a problem.
In tests performed on casings from bullets fired by a Webley Mk II revolver, the technique was able to reveal details such as fingerprint ridges and sweat pores – these could not be obtained via a commonly used cyanoacrylate fuming technique. And importantly, the ToF-SIMS method doesn't harm the fingerprints, leaving them intact for future analysis.
"This could really pave the way for a new reliable way to analyze evidence, identify persons of interest and link them to the ammunition in a firearm," says Sharp.
The research is described in a paper that was recently published in the journal Analyst.
Source: University of Nottingham