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Uncovering the Mysteries of Soil Forensics

Uncovering the Mysteries of Soil Forensics

Date Published: 11-Feb-15

Ever wondered how three grains of soil can catch a killer? We’ve dug up the facts on how soil forensics is uncovering the truth for investigators. 

Forensic science is based on Locard’s Exchange Principle, the idea that when two objects come into contact with another there is always an exchange of material. This exchange of material, no matter how small, can scientifically link suspects, victims and crime scenes to solve mysteries and investigate crime.

Soil forensics presents a diverse range of difficulties not usually encountered in environmental soil science. We dig down into the science of analysing soil evidence below:

  • The difficulties begin with the sample size; unlike soil samples taken for environmental purposes where the sample size can be as large as required, the sample size of a forensic soil case is often little more than a few grains of soil.
  • Because the samples are so minute and are evidence in a criminal investigation, non-destructive techniques must be used to preserve the evidence for further analysis.
  • Scientists analyse the fine fraction coating, a layer of very fine dust that coats grains of soil, rather than the grains themselves. This provides data that is more consistent with the location they originated from.
  • The current method of investigation uses x-ray diffraction to gain information on the characteristics and structure of the soil.
  • X-ray diffraction works by hitting a sample with an x-ray beam; the atoms in the sample scatter the x-rays and how they scatter provides information about the structure, characteristics and identity of the soil.
  • Soil science forensics has been used by investigators since the 1850’s, however, it wasn’t until 2000 that modern chemistry and analytical techniques used in environmental soil science, were applied to a forensic investigation.
  • The murder of two people in 2000 was the first case this was applied to. Police had identified a suspect, however were yet to locate the victims’ bodies. Soil scientists were able to match soil found on a shovel in the suspect’s car to a mining quarry where the bodies were discovered a mere 15m from the location scientists had indicated.

ChemCentre forensic scientists are often called upon by the West Australian Police to identify links between suspects, victims and crime scenes by examining and analysing evidence such as clothing fibres, glass fragments, soil grains and paint chips. More information on ChemCentre’s forensic services can be found here.

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