Police forensics could be able to DATE fingerprints for the first time

Scientists have found a way to date the age of fingerprints left behind on surfaces — such as at crime scenes — in a breakthrough that could transform police forensics. 

Fingerprinting has been a key tool for investigators since its broad uptake over a century ago — with each person’s pattern of arches, loops and whirls being unique. 

Recently, experts have placed much interest in mining fingerprint residues for chemical clues that might further help identify the individual who left them.

However, precisely narrowing down the exact time at which a given print was deposited had been proving elusive.

Such information could allow investigators to narrow down who was present in a given location at the time of crime based on fingerprints.

Chemists have now found that chemicals called triacylglycerols that are found in a person’s skin oils degrade in a predictable way that can be used to date fingerprints.

The breakdown rate, however, was found to vary between individuals — a muddling effect that will need addressing before fingerprint ageing can be used in the field.

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Scientists have found a way to date the age of fingerprints left behind on surfaces — such as at crime scenes — in a breakthrough that could transform police forensics

Researchers have now found that chemicals called triacylglycerols that are found in human skin oils degrade in a predictable way that can be used to date fingerprints 

A BRIEF HISTORY OF FINGERPRINTING 

Officials in Qin Dynasty China (around 221–206 BC) are believed to have taken hand and foot prints as evidence at crime scenes.

In around 1300 AD, the Persian physician Rashid-al-Din wrote of how no two individual’s fingerprints appeared to be alike.

University of Bologna anatomist Marcello Malpighi identified loops,  ridges and spirals in prints in 1686.

After the murder of MP Lord William Russel in 1840 (by his thieving valet), Dr Robert Blake Overton wrote to Scotland Yard advocating they use fingerprints to help identify the culprit.

However, the Metropolitan Police would not adopt fingerprinting until 1901, when French scientist Paul-Jean Coulier devised a method to transfer fingerprints from surfaces onto paper.

Fingerprints taken around 1859/1860

‘The unique features, or minutiae, of fingerprints have made them a trusted source of individual identification,’ Iowa State University chemist Young Jin Lee and colleagues wrote in their paper.

‘In-depth algorithms, such as those used in the automated fingerprint identification system (AFIS), are utilised to compare the unique features of an unknown fingerprint with those in existing databases.’

However, forensic officers at crime scenes presently have no precise way of telling whether a fingerprint was left behind during at the time of the corresponding crime or at some other point before or after.

In their study, the researchers investigated the reactions that take place in fingerprint residues as they slowly degrade with time.

This process occurs when ozone in the air reacts with the so-called unsaturated triacylglycerols — a type of ‘lipid’ biomolecule — which our fingertips leave behind on the surfaces we touch.

Using fingerprints left by three participating donors, the team used a chemical analysis technique called mass spectrometry imaging to track the changing levels of triacylglycerols over a period of a week.

The researchers found that they could reliably determine the rate of triacylglycerol degradation across the seven days of their study.

However, they also discovered that the rate of fingerprint degradation appeared to vary between the individual donors — with one of the print’s triacylglycerol levels being seen to decrease more gradually than the other two.

The team have attributed these differences to there being higher levels of other lipids in that individual’s fingerprints — which slowed the rate of triacylglycerol loss.

The team found that the dating method even works on prints that have been dusted with forensic powder.

Using fingerprints left by three participating donors, the team used a chemical analysis technique called mass spectrometry imaging to track the changing levels of triacylglycerols over a period of a week

Past research had shown that a that a gas chromatography–mass spectrometry method could determine whether prints were less than eight days old or not.

However,  but the newly-developed test affords the kind of more precise dating that investigators would need to be able to use such a tool in the field. 

With their initial study complete, the researchers are now moving to investigate how different environmental factors — such as the level of ozone or the local humidity — affect the degradation rates of fingerprint.

The team will also be conducting tests with a larger number of participants to help them better determine exactly how an individual’s fingerprint lipid levels impacts how fast triacylglycerol degrades and their prints fade. 

The full findings of the study were published in the journal Analytical Chemistry.