Forensic tech shows if fingerprints were applied to incriminating text

Even if someone’s fingerprints are found on an incriminating document, that person may claim that they only handled the blank sheet of paper before the real criminal printed anything on it. A new technique, however, can now be used to check if that really was the case.

Utilizing existing forensic tools, the process was developed by Loughborough University’s Prof. Paul Kelly and his former PhD student Dr. Roberto King.

Among other possible applications, it’s intended for use in cases of suspected fraud, wherein a person states they have no knowledge of a certain printed document. Although their fingerprints are on the paper itself, they claim that’s simply because they loaded the blank paper into a shared-use printer.

The investigational process begins by applying a thin layer of gelatine over any fingerprint that overlaps printed text on the document. That gelatine is then peeled off – lifting the fingerprint with it – and placed inside a vacuum chamber filled with disulfur dinitride vapor.

As that vapor reacts with lifted chemicals such as skin oils, the fingerprint becomes visible on the gelatine’s surface. If the fingerprint was indeed applied before the text was printed, the printed characters will be visible on the fingerprint, as the printer ink masked parts of it from the gelatine. On the other hand, if the fingerprint was applied after the text was printed, then the fingerprint will be complete, as none of it was masked.

Importantly, the lifted fingerprint and the original document remain intact, so they can be subjected to further forensic tests if necessary.

“Normal development techniques just reveal the presence of fingerprints, however this one allows us to show that you touched the document after the text had been printed,” said Kelly. “Of course, depending on the case, this could be good or bad for the defendant.”

A paper on the research was recently published in the journal Scientific Reports.

Source: Loughborough University

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