Forensic scientists have developed a new technique for pinpointing where soil found on a victim or a suspect came from. The method, which relies on DNA from bacteria in the soil, could be used to help prove that a suspect visited the site at which a body was dumped, for example.

""This allows you to take a soil sample from the shoe of a suspect or from the victim and tell where it came from originally,"" said Erin Lenz at Michigan State University in the U.S.
Soil found on a suspect's clothing or in the tread of a car's tires is frequently used as evidence in criminal cases. It can link a person or a vehicle to the crime scene.
""Soil samples can also ensure that a body or other evidence was not moved from another location, causing confusion as to the identity of the individual or in reconstructing the crime itself,"" wrote Lenz and her supervisor Dr. David Foran in the Proceedings of the American Academy of Forensic Sciences. Lenz presented her results at the academy's annual meeting in Washington DC this week.
Mass killings
The movement of bodies was a particular problem for forensic scientists investigating mass killings in the former Yugoslavia. The victims of mass killings were often moved from one large mass grave to several others in order to hide the true extent of the carnage.
In the past, scientists have used careful analysis of pollen and minerals in the soil to narrow down the location. ""However, these methods can very rarely pinpoint the exact location from which a sample originated,"" the researchers wrote.
Lenz and Foran used DNA from the bacterium Rhizobium for their method. This organism is frequently found in soil because it lives in the roots of some plants. So the profile of different Rhizobium types in the soil is a proxy indicator of the local vegetation. ""Some of them are present in all places, but you find other types that are common in only one,"" said Lenz.
The pair collected soil samples from five different habitat types in central Michigan, four of which were within 30 miles of each other, and found they could distinguish them using their ""bacterial fingerprint"".
Lenz said a lot more work would be needed before the technique passed muster in a courtroom. They don't yet know, for example, whether the fingerprints vary from season to season and they have not done enough sampling to be sure how unique each location's fingerprint is.
(Source: Guardian)