Every day, our feet go into our shoes without much thought. Yet, for a forensic analyst, the shoe can be a rich environment full of potential DNA evidence. On one hand, plantar skin cells can provide clues to the wearer’s unique identity. Each person has a unique bacterial colony on their feet and insoles. Through a foot swab, researchers can create a microbial DNA footprint of a suspect.
Your Bacteria Is Unique To You
A 2010 study by the University of Colorado found that 87% of the bacteria on a person’s body is unique that person only. “We found that each person seems to have a fairly unique compliment of bacteria that are personalized to themselves,” said lead researcher Dr. Christian Lauber. She said that even the cleanest criminals can’t get rid of this bacteria simply by washing. They found that the native microbial colony will return within hours of washing. Interestingly enough, there are restrictions on using fingerprints and DNA swabs without a warrant, but there are no such rules about using bacterial DNA yet, since the technology is so new. Early data suggests the new technique could be 70 to 90% accurate.
Challenges Of Relying On Foot Bacteria
However, analysts say shoes aren’t always the most reliable source of evidence. “Footwear that is used on a daily basis contains an abundance of bacteria that degrade DNA,” says the Forensic Science Division in Okinawa, Japan. “Further, numerous other factors related to the inside of the shoe, such as high humidity and temperature, can encourage bacterial growth inside the footwear and enhance DNA degradation.”
Shoe Exteriors Provide Clues, Too
It’s not just the material inside the shoes, but the material on the outside of the shoe, that matters in a crime. Researchers can assess trace amounts of soil to determine the microbacteria that is unique to particular areas. Soil type, color, particle size and chemical composition is assessed in the lab and compare the results to samples taken from several locations. Sure, there are limitations in this approach, but analyzing microbes is just another tool in the forensic scientist’s kit.