The sneakiest burglars slip by unnoticed, but they leave millions of their own witnesses at every crime scene. Researchers have found that it may be possible to identify criminals based on the microbes they shed from their skin or nostrils.
In 2014, at Argonne National Laboratory in Illinois and his colleagues showed that . This suggested that the microbes people leave behind could be useful for identifying suspected criminals like burglars. 鈥淲hat if we could potentially find signatures that are unique to each individual?鈥� says Hampton-Marcell.
He first visited crime scene investigators in Florida, who explained how burglars generally enter homes and how quickly local law enforcement responded. This varied from minutes to hours.
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Hampton-Marcell and his colleagues then arranged for 45 undergraduate students to carry out a series of mock burglaries at ten homes in Illinois and Florida, in August 2016 and March 2017. This gave the researchers a chance to look for deposits of microbes. Points of entry proved particularly fruitful. 鈥淭hey鈥檙e going to be using force, moving, likely shedding their microbiome,鈥� says Hampton-Marcell.
Spotted
The team analysed microbes from the skin and nostrils of every 鈥渂urglar鈥�. They used a genetic marker called 16S rRNA to distinguish the various microbes.
After sampling a total of 45 participants and gathering data from other studies, the team found they could group together thousands of unique sets of microbes that served as microbial fingerprints for individual people.
There was a detectable difference in the microbiome inside the homes after a mock burglary. The team found they could identify which mock burglar had entered the property with greater than 70% accuracy. 鈥淚 flipped out,鈥� says Hampton-Marcell. 鈥淚 literally fell out of my chair.鈥�
The research is being presented at in Atlanta, Georgia.
Decaying to nothing
鈥淚t鈥檚 an exciting step forward,鈥� says forensic scientist at Staffordshire University in the UK. Much like other forms of trace evidence such as DNA, the microbial data could help show that a burglar has rummaged around in a specific area like a jewellery box, she says.
However, there are several problems to overcome before the technique could be used in criminal investigations.
During the 2014 study, one of the homes was left empty for a few days while the occupants were away. In that time, their microbial signature disappeared. So unlike a fingerprint, Hampton-Marcell warns, the microbial signature left behind by a burglar will decay 鈥� starting just 30 minutes after they leave the crime scene.
However, that may be useful for revealing exactly when a burglary happened, provided samples can be taken quickly enough, says forensic scientist at University College London, UK. 鈥淚s there some way of determining the age of the deposit? That鈥檚 potentially a really valuable way of reconstructing events around a crime.鈥�
Hampton-Marcell also wants to improve the accuracy with which people are identified, ideally to 90% or better.
That would be good, says Morgan, but she adds that even 70% accuracy could be useful if fingerprint and DNA evidence were also available. The microbial data might not be enough on its own, but it would add to the weight of evidence. 鈥淚 can see how this, in combination with other forms of evidence pertinent in a specific case, could be an incredibly useful toolkit,鈥� says Morgan.
