Professor Lorna Dawson
The James Hutton Institute
Soil in criminal investigations: intelligence and evaluation in current and cold cases

Forensic soil science is an increasingly important discipline involving soils, minerals, dusts, plants and rock fragments to determine provenance i.e. to provide a chronology of their ownership, custody or location and as a comparison with a crime scene. Soil materials have been used as forensic trace evidence from early Roman times, and are often highly distinctive from one region to another 1. Such traces are extremely useful in a forensic context, because of their environmental specificity; their high levels of transferability; their ability to persist on items such as clothing, footwear, tools and vehicles; and their high levels of preservation after long periods of time. This resilience makes soil trace materials, often present at crime scenes and forensic exhibits, highly valuable forms of intelligence and evidence that can aid crime investigations and scenario reconstructions. Significant advances in forensic geoscience over the past decade, in the development of analytical approaches, miniaturisation and also in understanding the behaviour, transfer, persistence and preservation of sediments, soils and plant material have widened their applicability and evidential value. Evidence samples can be analysed using a wide range of complementary methods that address their physical, chemical and biological components with greater precision, speed and accuracy than ever before. This now permits samples of less than 10 milligrams to be accurately characterised, and permits forensic soil science to also contribute to cold case investigations, both in providing intelligence and evidence in court. Examples will be presented of case work where soil has played a pivotal role.

Sediments/soil on footwear and vehicles can indicate where a crime may have taken place, and may provide evidence of a person being at a particular place of interest. Improved analytical capabilities, coupled with the development and availability of relevant databases, allow forensic geoscientists to help police to search for unknown objects or people, prioritise areas for investigation or search, and provide robust and reliable evidence in court. Forensic geoscience has mainly been used in the past in the context of high-impact crimes such as murder, rape, aggravated burglary and terrorism investigations, where resources allow it. However, techniques are becoming cheaper and faster, and have the potential to become regularly used. With developments in analytical technology, and an increasing understanding of how soils and sediments are distributed within natural and anthropogenic environments, forensic soil science has more power to answer questions such as: “Where did the soil material come from?’, or “Where has this item been?”. Understanding (and effectively communicating) the context of a specific case is crucial to help answer such questions. In addition, being able to explain the significance of the evidence that has been analysed, and demonstrating logically and transparently how a conclusion has been reached, remains important for forensic soil science specifically and trace evidence generally.

1 Dawson, L.A., Mayes, R.W., 2015. Criminal and Environmental Soil Forensics. In: Murphy, B.L., Morrison, R.D. (Eds.), Introduction to Environmental Forensics, pp. 457–486.