DNA-Shedder Status May Impact Crime Scene Investigations

If you’ve ever watched CSI, you know that suspects often leave incriminating DNA traces at crime scenes. However, a recent study suggests that the amount of this genetic material could also indicate a person’s guilt or innocence.

The Role of Touch DNA in Crime Scenes

Although we usually think of crime-scene DNA as coming from bodily fluids like blood and saliva, a large portion actually consists of shed skin cells that transfer to objects a person touches. We refer to this material as “touch DNA.”

You might assume that a higher amount of touch DNA at a crime scene indicates a greater likelihood of the person’s involvement in the crime. However, research from Flinders University in Australia shows that this is not necessarily the case.

Led by Prof. Adrian Linacre, forensic scientists had 100 volunteers of various ages and genders press both thumbs onto glass slides at timed intervals (up to three hours) after initially washing their hands.

Collecting and Analyzing Skin Cell Samples

As each person pressed their thumbs onto the glass, they left some skin cells behind. Researchers took three samples from each thumb at each interval, and each volunteer performed the test once a day for three consecutive days. By applying dye to the samples, the researchers counted the number of cells each person left on the slide during each test.

They found that 98 out of 100 participants consistently left roughly the same number of cells on the glass at each interval and each day.

Classification of Volunteers into Cell-Shedding Categories

The scientists classified the volunteers into five categories of cell-shedding: light, intermediate-light, intermediate, heavy-intermediate, and heavy. This finer categorization is more detailed than a 2022 study with just 11 subjects, who were classified into low, intermediate, and high cell-shedding categories.

With these findings, defense attorneys might argue that the high amount of their client’s DNA at a crime scene is due to the client being a heavy shedder.

They might also argue that the client couldn’t have been at the crime scene for the time stated by the prosecution, as more or less DNA would have been left behind. Additionally, if the DNA match is uncertain, the quantity could either strengthen or weaken its connection to the individual.

Depending on what type of ‘shedder’ a person is, confirming their shedding status can help investigators understand how likely it is that an individual’s DNA will transfer to an item through hand contact, says Linacre. “This information can be used in a likelihood ratio to assess the probability of finding a person’s DNA on an item.”

Read the original article on: New Atlas

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