Soil and some of its darker secrets
Professor Lorna Dawson, Environmental and Biochemical Sciences, James Hutton Institute
A key resource for food security and human sustainability, soil science is truly interdisciplinary in nature with soils varying in their physical, chemical and biological characteristics, along with obtaining other information, such as diatoms, pollen grains, trace plant debris, all potentially of help to the investigative process. Such information can help both in the investigative stage of an investigation (intelligence) such as in the search for a missing person, and also can provide trace evidence (evaluative) and ultimately be presented as evidence in court. Soil is not just mud or dirt.
The main types of questions I get asked are: "where could that soil have come from?" as I examine a spade from a suspects boot, or "can that soil be evidentially linked to that crime scene?" as I interpret the data obtained through a series of analyses with a comparison of soil from a questioned item such as footwear or a vehicle with soil from a locus and alibi sites. No two cases are ever the same, with case context of vital importance, with different contextual samples being required in each case.
Soil is a complex and heterogeneous material involving customary contact with persons, vehicles, tools and objects. That complexity can make it an important form of contact trace evidence in crime investigation. Field survey, geographical information systems (GIS) and an understanding of the landscape and the relationships between soil, hydrology, vegetation and geology is central to developing search strategies in the field. We can subsequently adopt a wide range of analytical approaches to collected soils. Soil is unlikely to be the only form of evidence used in an investigation, but it can be very powerful when brought strategically together with other pieces of information.
Soil mineralogy, organic characterisation, botany, diatom, fungal and nematode identification, plant and seed DNA analysis, and bacterial DNA profile characterisation are some of the main characteristics that are currently used in case work. A wide range of state-of-the-art methods are at our fingertips at the James Hutton Institute: X-ray diffraction, infra-red spectral analysis, gas chromatography, Scanning Electron Microscopy, and light and heavy isotope analysis, all which have been used to great effect in many cases. Geographic Information Systems have been developed at the Institute, to allow the mapping of exclusion of areas in search, enabling police to fine-tune areas on the ground for missing persons or objects and have assisted in police search operations.
In addition, physical features within a soil sample such as hairs, fibres, flakes of paint, plastic shards and even flakes of skin have been identified, held within a soil aggregate, and can be characterised thus contributing to the evidential value of a soil sample. Vehicles, footwear, clothing, spades and tools, as well as trace amounts of material, e.g. found under a fingernail, can be examined and analysed in the James Hutton Institute laboratories, potentially turning round a sample analysis and interpretation in less than 24 hours. Soil also contains a range of clues such as volatile organic compounds, cholesterol and DNA, that can help suggest the presence of human material which assist police in the location and recovery of bodies.
No two police investigations or forensic cases are ever the same; the approach adopted depends on the question asked and the case situation and context. When I am contacted by the investigating authorities, I consider each individual case context and individual questions asked, and then decide upon the most appropriate approach to take. Visiting the site can be very revealing, offering up potential solutions as to where to take the most appropriate control samples. The first laboratory stage in any case is to carefully examine the reference soil and soil or traces of vegetation on any questioned items such as footwear, vehicles or objects associated with a potential crime scene. The microscope is one of the most important tools, often revealing secrets that can link that questioned item back to having been in contact with a specific locus.
In Roman times, soil on the hooves of enemy horses was examined to ascertain which area they had ridden from, thus informing them as to the location of the oppose forces. Metal theft, murder, rape, burglary and assault are the main types of crime where soil is used as evidence in current times. Soil has been used as part of many recent high profile court cases, such as in the double murder of Jessica Chapman and Holly Wells in Soham, the death of businessman Ali Jawaid, who was struck with an iron bar outside a mobile phone shop in Coventry, the search and recovery of Pamela Jackson from Durham, and the double murder of Helen Scott and Christine Eadie from Edinburgh.
This soil information can now be made available to the investigator relatively easily. The development and implementation of novel and evolving technologies, such as genetic information, through microbial DNA will enable the more routine use of soil in investigations, whether in a civil or criminal legal context, and thus bridge a security gap, benefiting civil UK, European and global security.
Effective communication is vitally important both at the initial case question, through the case conference stage along with investigators, to the presentation of evidence through the Criminal Justice System in court. DNA from ‘dirt’, along with soil mineral and organic characteristics, can provide vital clues about how death might have occurred or help investigators work out how crimes have been committed, ultimately helping to complete the investigative jigsaw of crime investigation.
This article was originally published in the Summer 2015 issue of The Geographer, the magazine of the Royal Scottish Geographical Society, and has been reproduced by kind permission of the RSGS.
