PhD candidate Emily Bibbo and Mariya Goray at the DNA forensics research room at Flinders University.
Using environmental DNA (eDNA) as forensic evidence in criminal cases may be a newer idea; but the general concepts goes all the way back to Edmond Locard in the 1930s. Locard's Exchange Principle states that with contact between two items, there will be an exchange of microscopic material. This sort of trace evidence is more valuable than ever in today’s forensic investigations given the sensitivity of modern DNA analysis techniques.
Researchers at Flinders University in Australia have now taken this one step further by using a new technique to potentially pick up and record airborne forensic DNA evidence from crime scenes wiped clean of fingerprints and other trace evidence.
The new study, published in Electrophoresis, focuses on collected DNA from air conditioner units that circulate air around a room, as well as different kinds of filters at different periods of time.
“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,” said study author Mariya Goray, senior lecturer in forensic science at Flinders.
The small-scale pilot project compared results from samples taken from air conditioners in four offices and four houses at different time frames after cleaning. Researchers also looked at the possibility of collecting human DNA from air in rooms, with and without people for different periods of time and with different types of collection filters.
Results 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.
“We now know that eDNA shed from sources, such as skin or saliva can be detected in the environment, including soil, ice, air and water,” said Goray. “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.”
Despite the promising results, Goray and team recommend follow-up studies to determine the best location for air collection devices, and the appropriate time after a crime to test and acquire DNA—if present.
Collection of trace DNA is becoming increasingly important in criminal investigations. For example, 62% of all samples processed by Forensic Science SA (Australia) in 2020 were trace or touch evidence—yet success rates with this type of evidence remain poor.
Still, it’s not the researchers’ first time working with eDNA. In 2020, forensic scientists at Flinders University received a grant to develop a system to trace the source of dust on suspect articles to match a soil profile of a specific area or overseas country in the interest of counter-terrorism and national security.