Your DNA shedding status could be crucial in the crime scene investigation

If you have ever seen CSIDo you know that suspects often leave incriminating DNA traces at crime scenes. According to a recent study, the telltale Crowd This genetic material could also indicate a person’s guilt or innocence.

We may think that crime scene DNA is usually found in bodily fluids such as blood and saliva, but much of it is in the form of shed skin cells that are transferred to objects a person touches. This material is therefore called “touch DNA.”

You might think that the more touch DNA found at a crime scene, the more likely it is that the person was involved in the crime. However, according to a study from Australia's Flinders University, that's not necessarily the case.

Led by Prof. Adrian Linacre, a team of forensic scientists asked 100 volunteers of different ages and genders to press both thumbs onto glass slides at specific intervals (up to a total of three hours) after washing their hands.

Each person transferred a portion of their skin cells to the glass. Three samples were taken from each thumb at each interval, with each person performing the test once a day for three consecutive days. By then coating the samples with a dye, the researchers were able to count how many cells each person left on the slide during each test.

First, it was found that 98 of the 100 test subjects left approximately the same number of cells on the glass at each interval and on each day.

In addition, the scientists found that based on these numbers, each of the volunteers fell into one of five cell shedding categories: mild, moderate, moderately severe, severely moderate and severe. This is a finer differentiation than that achieved in a 2022 study with only 11 test subjects who fell into the categories of low, moderate and severe cell shedding.

Given this new evidence, defense attorneys could potentially argue that the only reason so much of their client's DNA was found at the crime scene was because the person was randomly shedding DNA heavily.

They could also argue that their client could not have been at the crime scene for the period of time stated by the prosecution because in that case more – or less – of his DNA would have remained. And if the DNA itself was a dubious match, the amount of that could be used to strengthen or weaken the connection to a particular person.

The data could even be used to exclude suspects before the cases even go to court.

“Depending on what type of 'shedder' a person is, confirming their shedder status can give investigators insight into a person's propensity to transfer their DNA to an object through hand touch,” says Linacre. “This information can be used in a likelihood ratio to assess the likelihood of finding a person's DNA on an object.”

An article about the research was recently published in the journal Forensic Science International Genetics.

Source: Flinders University via EurekAlert