Wednesday, November 25, 2020

Fingerprint breakthrough in determining sequence of deposition of fingerprints on printed paper

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Michael Whyte
Crime Scene Officer and Fingerprint Expert with over 7 years experience in Crime Scene Investigation and Latent Print Analysis. The opinions or assertions contained on this site are the private views of the author and are not to be construed as those of any professional organisation or policing body.
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For more than a century, fingerprints have been crucial to the investigation of crime and are still responsible for more identifications than DNA evidence.  Now, a University of Huddersfield researcher is responsible for breakthroughs that will make fingerprinting a more valuable forensic tool than ever.  Fraudsters are among the offenders who will be easier to detect, thanks to the work of Dr Benjamin Jones.

‌The article describing the successful research project was published in Science and Justice, which is the journal of the Chartered Society of Forensic Sciences.  It was then selected for the P.W. Allen Award, which is bestowed by the editor of the journal and the council of the Society on the paper adjudged to be the best of its year.

Dr Jones headed a team that has discovered a technique for taking fingerprints from laser-printed paper and – crucially – detecting whether or not the mark was made before or after it was printed on.

Detection of fingerprints on paper can be a somewhat complicated process due to the chemistry and makeup of the surface morphology coupled with the rapid absorption of components from the surface of the paper, which occurs within seconds after deposition. Penetration and lateral absorption of fingermarks also depend on the chemical components of a deposited print, which varies in relation to the person, their emotional state, food consumption and grooming regime. Studies have shown that depth of penetration of fingermarks varies with types of paper, with a good correlation between penetration depth and quality of chemically developed prints.

Establishing the depth of penetration of prints into surfaces, as well as order of layers in, for instance, overprinting with text or images, can provide considerable assistance to crime-scene investigations by providing an insight into the history of documents for forensic studies. In cases such as fraud or counterfeiting it can be imperative to know whether a fingerprint has been deposited before or after the paper is printed with compromising material, and therefore be able to assess whether a suspect is associated with the printed evidence.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) in particular is one of the most sensitive of all laboratory surface analytical techniques, showing potential in the examination of fingerprints for analysis of constituent metals and contaminants present. ToF-SIMS provides detailed chemical and spatial information of the top few nanometres of a surface, and has shown its ability to capture images and extract chemical data in a minimally invasive manner, with only the first two monolayers being ablated off a surface. This implies that the integrity of the print is not entirely compromised, and should potentially allow for additional extraction of information from the fingerprint, an important factor in forensic investigations.

Schematics of Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

As a demonstration of proof of concept, blind testing of 21 samples from three donors resulted in a 100% success rate. The sensitivity of this technique was investigated within this trial through the examination of up to fifth depletion fingerprints and ageing of up to 28 days. Migration of fingerprint and paper components to the ink surface, although observed with increased ageing time, was not found to compromise determination of the deposition sequence.

Source: University of Huddersfield

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