Fingermarks method gives boost to forensics

The method will allow observation of fingermarks from objects such as bullet casings with greater detail and accuracy than traditional forensic methods.

Scientists from Nottingham University’s School of Physics and School of Pharmacy have developed a rotation stage to allow researchers and forensic practitioners to perform highly sensitive, non-destructive Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) measurements and develop high-resolution fingerprint images on surfaces that conventional fingerprint imaging fails to pick up. The rotation stage is claimed to open up new possibilities for the retrieval of high-resolution fingerprints from the whole surface area of challenging shapes and materials.

“We already proved in our previous research that ToF-SIMS imaging provides much more accurate and detailed fingerprint images on different types of surface,” Dr James Sharp, School of Physics and Astronomy, said in a statement. “This new rotational capability allows us to image in even more detail and over whole surface areas of difficult materials and shapes whilst keeping the evidence intact.”

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According to the University, retrieving fingermark evidence from bullet casings presents major challenges for forensic scientists. Fired and unfired casings can often be found at the scene of violent crimes, but retrieving fingermarks and linking the person that loaded the gun to the crime is difficult because of the physical conditions experienced by the bullet casings during firing and techniques that are used to retrieve the fingermarks.

When a bullet is fired, the casing experiences high temperatures, pressures and large friction forces inside the barrel of the gun. They can also be coated by the residues of propellant and the powder that are used to generate the reaction that forces the bullet out of the chamber. These combined effects often result in the removal, evaporation or degradation of the more volatile components of fingermark residue (such as water, amino acids, and lipids), plus potential smudging or obscuring of the mark. These factors can make it difficult for retrieval methods such as cyanoacrylate (superglue) fuming and fluorescent staining to work.

ToF-SIMS is a sensitive surface-analysis technique that the Nottingham team said provides very detailed information about the locations of different chemicals on a surface. The technique uses high-energy (up to 30keV) beams of positive ions directed at the sample’s surface to free secondary ions from any material that they collide with. These ions are accelerated into a time-of-flight analyser and separated according to their mass-to-charge ratio, producing a spectrum that is indicative of the sample’s chemical composition.

Images generated using ToF-SIMS were shown to display evidence of friction ridge and sweat pore level detail on samples where fingermarks were not visible when developed using cyanoacrylate and the dye Basic Yellow 40 (BY40).

Experiments performed over seven months determined how fingermarks deposited on the surface of Webley MkII revolver rounds change over time. The ToF-SIMS technique is also non-destructive and no evidence of image degradation was observed over this period, even when samples were repeatedly exposed to UHV conditions.

“This could really pave the way for a new reliable way to analyse evidence, identify persons of interest and link them to the ammunition in a firearm,” said Dr Sharp.