In criminal investigations, detectives collect and analyze evidence found at the scene to reconstruct the events and individuals involved in the crime. The “principle of exchange” formulated by criminologist Edmond Locard states that every contact leaves a trace, forming the basis for reconstructing events. Traditionally, traces were visible materials like pollen and fibers, but these are limited in identifying specific individuals. However, recent research has shown that the population of bacteria on a person’s skin leaves traces on their clothes that can be used to uniquely identify them.
Microbial traces are specific to an individual and can persist over long periods of time, making them useful in forensics. Forensic microbiology, which emerged in the early 2000s, is used to identify individuals after death, understand their health before death, determine cause and time of death, and trace their origins. The updated version of Locard’s principle is that every contact leaves a microbiological trace.
While this principle is established, there is still much to learn about the transfer and persistence of an individual’s microbiome on their surroundings. Researchers also want to understand how microbial traces can be contaminated and how different surfaces affect microbial populations. Previous studies have shown that bacterial populations on individuals’ skin can be transferred and persist on non-porous surfaces for up to a month.
In a recent study, researchers focused on identifying individual microbiomes from clothing, which is often collected as evidence at crime scenes. They had two individuals wear cotton T-shirts for 24 hours, then placed the T-shirts in a controlled environment for up to six months. Samples were taken from both worn and unworn T-shirts at various points in time and analyzed for microbial DNA. The results showed that distinct and recognizable microbes from each individual were transferred onto the clothing, and the microbiome remained stable on the worn garments for up to 180 days. They also observed the transfer of specific bacteria from worn items to unworn ones stored nearby.
Clothing plays a crucial role in criminal investigations, providing evidence for profiling individuals and reconstructing events. The discovery of unique microbiomes capable of identifying individuals from clothing is a significant advancement in forensic science.
