Guidelines for Criminal and Environmental Soil Forensic Investigations.

No standard forensic soil examination approach, method or guidelines exists. The main reasons for this are that examination of soil is concerned with detection of both naturally occurring soils (e.g., minerals, organic matter) and anthropogenic soils that contain manufactured materials (e.g., brick fragments). Hence, forensic soil examination can be complex because of the diversity and heterogeneity of soil samples that can be encountered. Such diversity and heterogeneity have enabled forensic soil examiners to distinguish between soils, which may appear to be similar.

The experience gained from conducting over 70 case studies, together with research by the Centre for Australian Forensic Soil Science (CAFSS) has led to the development of “guidelines for soil forensic investigations”. Guidelines were developed and designed to provide a “systematic approach” for examining and characterising soils for forensic comparisons, which involves subdividing methods into the following 4-stages each comprising several steps and involving a combination of techniques:

1. Morphological characterisation of composite soil particles in whole soil samples for screening of samples.

2. Identification, characterisation and semi-quantification of minerals and organic matter in composite and individual soil particles following sample selection and size fractionation (< 50 µm).

3. Detailed characterisation and quantification of minerals and organic matter in composite and individual soil particles following sample selection; size or magnetic or heavy mineral fractionation using advanced analytical methods.

4. Landform and soil mapping; construction of soil-regolith conceptual models.

The progression of a soil forensic examination through each of the four stages will depend on a number of factors such as the amount of sample available and the results from the early stages of the examination. The guidelines describe best practice for field (collecting, identifying and describing soil samples) and key laboratory techniques, which requires consistent and correct use of terms and standard methods. This approach has enabled soil properties to be successfully used to both discriminate between or match soils for critical evidence to solve overwhelmingly complex criminal and environmental forensic cases.