FORENSICS:SOIL IS not just dirt beneath your feet – it can be crucial in investigating crime.
Prof Lorna Dawson of the James Hutton Institute in Scotland has used evidence from soil in cases of murder, burglary, drowning and even for proving the provenance of garlic!
Prof Dawson is a member of the newly established Forensic Geology Initiative organised by the International Union of Geological Sciences.
The initiative brings together experts on soil forensics from around the world, and will unify the guidelines for tests, she told the British Science Association festival. She works with police on crime investigations at international level.
She was one of the first scientists to bring together all the techniques to forensically examine soil.
“Soil is very complex; it is the very nature of that complexity that means it can be used to give precise information,” she said.
Soil is useful in crime investigations because it is sticky and location-specific. It will stick to anything that has come into contact with it – ie a suspect’s shoes or car tyres.
Scientists can check signatures in a soil sample to see if they match the soil at a crime scene.
The types of minerals, size and shape of sand particles and even the natural etchings on individual sand grains can be specific to a type of soil.
When working with police on a murder investigation, Prof Dawson was able to show that the sand found on car tyres was the same type of sand as that at the grave of a murder victim. This was used as evidence that the suspect could have been at the murder site.
Different soils are also home to different micro-organisms. Scientists test the genetic evidence from bacteria in the soil to see if they are the same as the bacteria at the crime scene.
All this information is used to work out where a sample of soil has come from, and so gives a likelihood that a suspect had, or had not, been at the crime scene.
Of course, most soil is not unique to a single location, and scientists have to check soils at neighbouring sites to see where else the sample could have come from.
Scientists also examine things found in soil. In a burglary investigation Prof Dawson found dog hair from the burgled house trapped in mud on the suspect’s shoes.
She has also found carpet fibres, plastic and bits of plants in soil samples. These objects can be as useful to forensics as the soil itself.
Prof Dawson says soil forensics is used as part of the evidence in a trial, but when used with a combination of physical and biological information it can be powerful.