If you've ever watched Crime Scene InvestigationYou know that suspects often leave incriminating DNA traces at crime scenes. But according to a recent study, this amount The presence of this genetic material may also indicate whether a person is guilty or not guilty.
While we usually think of crime scene DNA as being found in body fluids like blood and saliva, much of it is in the form of shed skin cells and is transferred to items a person touches, which is why this material is called “touch DNA.”
You might assume that the more touch DNA an individual has at a crime scene, the more likely that person is involved in the crime. But according to research from Flinders University in Australia, that's not always the case.
A team of forensic scientists led by Prof. Adrian Linacre asked 100 volunteers of different ages and genders to press both thumbs onto glass slides at set intervals (for up to three hours in total), after initially washing their hands.
In doing so, each person transferred some of their skin cells to the glass. Three samples were taken from each thumb at each interval, and each person performed the test once a day for three consecutive days. By then applying a dye to the samples, the researchers were able to count how many cells each person left on the slide in each test.
First, it was found that 98 out of 100 subjects left approximately the same number of cells on the glass at each interval and each day.
What’s more, based on these numbers, the scientists determined that each of the volunteers fell into one of five categories of cell shedding: mild, moderate-mild, moderate, heavy-moderate, and heavy. That’s a finer distinction than a 2022 study that included just 11 test subjects who fell into the categories of low, moderate, and heavy cell shedding.
With these new findings in mind, it's possible that defense attorneys could argue that the only reason their client's DNA would be found at a crime scene is because the person sheds a lot of skin.
They may also argue that their clients could not have been at the crime scene within the time frame the prosecution stated because if they had been, more or less of their DNA would have been left behind. And if the DNA itself is an uncertain match, the amount his It can be used to strengthen or weaken a connection with a particular person.
The data could even be used to eliminate suspects before cases reach court.
“Depending on what type of 'shed' a person is, verifying their shedding status can guide investigators as to an individual's propensity to transfer their DNA to an object through hand contact,” Linacre says. “This information can be used on a probability ratio to assess the likelihood of finding an individual's DNA on an object.”
An article on the research was recently published in the journal Forensic Sciences International Genetics.
Source: Flinders University via EurekAlert