Could air conditioners be key to crime solving?

AUSTRALIA: Air conditioning units may in the future be used by forensic teams to access vital DNA evidence in crime solving.

A new study led by researchers at Adelaide’s Flinders University explores new techniques to potentially pick up and record key airborne forensic DNA evidence from crime scenes wiped clean of fingerprints and other trace evidence.

“Human DNA can be found in the air after people have spoken or breathed (via saliva droplets), shed skin cells or dislodged and aerosolised from surfaces and collected for DNA analysis,” explained Emily Bibbo, a PhD candidate at Flinders University’s College of Science and Engineering.

“We may be able to use this as evidence to prove if someone has been in the room, even if they wore gloves or wiped surfaces clean to remove the evidence.”

Collection of trace DNA, comprising just a few human cells, is commonly used in criminal investigations, yet success rates with this type of evidence remain poor, the researchers say. 

However, new technologies are providing new avenues for evidence collection – including the emerging field of environmental DNA (eDNA) from solid surfaces, soil, water and air.

The pilot study, conducted in collaboration with international experts, focused on additional avenues for DNA collection by investigating air conditioning units as well as different kinds of filters at different periods of time to compare results.

Flinders University senior lecturer in forensic science Dr Mariya Goray says biological material is routinely collected from crime scenes and exhibits, and these new methods have the potential to help identify the usual users of a room as well as visitors.

“It is very unlikely that an average offender, even with forensic awareness, could totally prevent their DNA from being released into the environment,” Dr Goray said.

The small-scale pilot project compared results from samples taken from air conditioners in four offices and four houses at different timeframes after cleaning. The other research looked at the ability to collect human DNA from air in rooms, with and without people for different periods of time and with different types of collection filters.

Results from the studies show that human DNA can be collected on the surfaces of air conditioner units and from the air, with air samples likely representing the more recent occupation while previous users of the room were  more prevalent in air conditioning units.

The article, Up in the air: Presence and collection of DNA from air and air conditioner units (2024) has been published in Electrophoresis.