Soil forensics aid in Tasmanian murder case

Tasmania has a very diverse range of soil formation environments due to wide variations in geology, landforms, landscape history and climatic setting. Parent materials range from mafic to highly siliceous, with some carbonates; mean annual rainfall from 400 to 3000 mm/year while soil formation periods range from a few thousand to several millions of years. This setting leads to a wide range of soil types with vastly differing mineralogy, chemistry and stratigraphy occurring in relatively close proximity. This diversity can assist in criminal investigations and prosecutions via soil evidence helping to both eliminate and/or locate crime scenes from an investigation or to support presence or absence of incriminating additions or modifications to soil materials. We used X-ray diffraction and a sequence of soil profile descriptions at a crime scene to show earthy lime rich materials found above the murder victim in a deep pit (4 m) were exotic to that environment. The local soil type, in which the victim was located, was a very deep Acidic Red Ferrosol formed from dolerite in the Tasmanian highlands. The subsoils of the soil profiles described adjacent to, upslope and down slope of the murder site had acid reaction (pH < 5.0), were deeply weathered, clay textured and red to dark reddish brown in colour. X-ray diffraction analysis undertaken identified the light coloured, highly alkaline (pH 11.8) lime rich materials as being composed of 90 – 95% calcium carbonate with traces of calcium hydroxide (“lime”). These properties supported the incompatibility of the “lime” with the soil, showing it to be exotic to the site. This fact helped to link the perpetrators to the crime scene.