Secrets in the air: Scientists test dust as crime scene tool

Criminals beware – while you could wipe off fingerprints, the very air around you might be giving you away.

At least that’s according to researchers who are investigating how dust can vary between locations, potentially uncovering important clues for where a crime was committed.

“Dust is found everywhere,” says Dr Nicole Foster, who undertook the work at Flinders University and is currently a researcher at the Smithsonian Environmental Research Institute in the USA. 

“It stays on clothing and items after you have travelled and leaves a trace for where you have been.”

The research has been published in Forensic Science International: Genetics.

Environmental DNA or eDNA is a type of DNA sampling tool which measures tiny fragments of genetic material from waterways, sand, dust, and even air. These samples can tell researchers what type of animals, humans, or even bacteria or fungi are in the area.

For this experiment, the team hypothesised that different locations would have different eDNA profiles due to the mix of bacterial and fungal communities. Different eDNA profiles – along with chemicals local to the area – would mean that specific dust would have a specific location it could be matched to.

“The airborne fraction of soil [dust] is both ubiquitous in nature and contains localised biological and chemical signatures, making it a potential medium for forensic intelligence,” the researchers write in their new paper.  

“Metabarcoding of dust can yield biological communities unique to the site of interest, similarly, geochemical analyses can uncover elements and minerals within dust that can be matched to a geographic location.”

To do this, the researchers placed a number of small, raised tiles at three locations in South Australia – Deep Creek Conservation Park, Brookfield Conservation Park and Hale Conservation Park.

After 1, 4, 8, and 12 weeks, tiles were swabbed and analysed to see what was picked up.

Then they tried to see if they could match a sample to its location.

“From the dust samples collected from around South Australia, we were able to correctly predict provenance for 67% of samples using bacteria profile and 56% using fungi profiles,” says co-author Dr Duncan Taylor, a forensic DNA scientist.

“It’s likely this biological variation within each site led to this level of incorrect predictions but we observed the within-site variability was not greater than between sites.”

These results are not foolproof, and the team acknowledge that they did make it easier for themselves by ensuring the samples were protected from the elements. Further research will need to be done to confirm this could be used effectively in a wider range of conditions.

“We found that the dust recovered from each item contained chemical and biological profiles that were unique to sites, but these profiles were variable within sites and over time,” said Foster.

“This work is a proof of concept for using dust as a medium in forensic intelligence, but more work needs to be done before integrating this tool for forensic casework.”