DNA In Air Could Thwart Criminals Trying To Evade Detection By Cleaning The Scene

We could soon be catching criminals using an entirely different kind of DNA sampling approach that tests for evidence in the air. Forensic-savvy criminals may know to wipe down the scene if they want to get rid of damning DNA evidence – but both the air itself and air conditioner units can still hold incriminating clues.

Forensic technology capitalizes on the fact that we leave a trail of DNA everywhere we go, from saliva when we speak and cough, to dead skin cells, and even rootless hair can yield DNA, something that was previously thought to be impossible. Criminals have been identified using DNA, such as from discarded napkins and semen samples, for decades, helping solve countless cases. Wearing gloves and cleaning surfaces can get rid of some of this precious evidence, however, so finding environmental DNA (eDNA) through other means can be pivotal in cases involving forensic-savvy criminals.

A new small-scale investigation looked to two key places to find eDNA; air conditioners that were recycling air in four offices and four houses, and the air of rooms themselves. The spaces were tested at different intervals after cleaning and with different numbers of people having occupied the space for different amounts of time.

The results showed that human DNA can be found in both settings. The DNA collected from the air was representative of more recent occupation, while that taken from the surfaces of air-conditioner units was typically a bit older. This means the place where the eDNA is found can tell us about how that person was using the space.

“This study showed that human DNA can be collected from air and on surfaces that move air, such as air conditioner units, and can identify the usual users of the space as well as frequent visitors,” wrote the authors. “Sampling of air conditioner units may be used to identify usual or long-term occupiers of a space, and air sampling may assist in the identification of short-term or recent users of a room. Such sampling may be considered, for example, if it is suspected, gloves were worn or that the crime scene has been cleaned post incident.” 

While a promising step towards thwarting criminals’ attempts to evade forensic detection, the authors say further research is needed to establish the best places to test for air collection within different spaces as, if DNA is present, it’s not always going to crop up in the same places. So gloved criminals, beware. The science isn’t going to make it easy for you.

“It is very unlikely that an average offender, even with forensic awareness, could totally prevent their DNA from being released into the environment,” said Flinders University Senior Lecturer in Forensic Science Dr Mariya Goray in a statement. “We now know that eDNA (environmental DNA) and eRNA shed from sources such as skin or saliva can be detected in the environment, including soil, ice, air and water.”

The study is published in the journal Electrophoresis.

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