Gazette - Getting the dirt

EXTERNAL SUBMISSION

By Dr. Rob Fitzpatrick, Director, Centre for Australian Forensic Soil Science

The value of soil in criminal investigations

Soil forensics is the science or study of soil that involves the application of a wide range of soil information to answer legal questions, problems or hypotheses.

For soil scientists, soil is made up of different sized mineral particles (including sand, silt, clay and organic matter) and has complex biological, chemical, physical, mineralogical and hydrological properties that are always changing over time.

But for farmers, gardeners and agronomists, soil is just a medium for growing crops, pastures and plants. And for engineers, soil is a material to build on and excavate.

Thus soils can be both naturally occurring, comprising natural minerals and organic materials, and man-made, such as those that often contain very small amounts of manufactured materials, including brick fragments, explosive residues or paint flecks.

It is this soil diversity and heterogeneity that has enabled forensic soil examiners to distinguish between soils that may appear to be similar to the untrained observer.

History

Soil forensics dates back more than 150 years. Arguably, the first documented case of a forensics comparison of soils took place in Berlin and was used to help police solve a crime that took place on a Prussian railroad in April 1856.

A barrel that had contained silver coins was found on arrival at its destination to have been emptied and refilled with sandy soil. Prof. Christian Gottfried Ehrenberg in Berlin acquired samples of the soil from all the stations along the line.

Using a light microscope, he examined features of the soil particles, such as colour and shapes, to compare the soil similarity in the barrel to the station from where the sand originated.

In October 1904, George Popp, a forensic scientist in Frankfurt, successfully examined soil, minerals and dust from clothes for identification to help solve a criminal case.

Between 1905 and 1990, soil information was used extensively by police. However, by that point, soil analysis became too specialized and expensive for in-house use in most Australian forensic laboratories and outside forensic agencies.

As a consequence, critical soil forensic evidence was often missed or ignored completely, hidden amongst trace evidence and insufficiently analyzed. And new techniques in soil science were not deployed on complex forensic cases.

Today

A double murder in 2000 helped bring forensic soil science back to the forefront. Soil scientists from the Australian Commonwealth Scientific Industrial Research Organization (CSIRO) used soil properties including colour as well as chemical, physical and mineralogical characteristics as well as soil maps and field investigations to solve the case.

Scientists identified similarities between soil found on a shovel taken from the suspect’s vehicle and soil subsequently located in a gravel quarry. The identical samples were undeniable and later helped reveal the location of the two buried bodies.

This success led the Australian forensic community and CSIRO scientists to establish the Centre for Australian Forensic Soil Science (CAFSS) in 2003.

The centre is the first worldwide network of forensic and soil scientists to maintain a critical mass of expertise in soil forensics to help protect Australia from crime, terrorism and environmental pollution.

CAFSS expertise spans five disciplines: soil profiling (collection of samples from scenes of crime, soil descriptions and soil mapping), minerology (x-ray diffraction), chemistry, soil biology/molecular diagnostics (soil organics and soil DNA) and soil geophysics (electromagnetics and ground-penetrating radar).

The personnel in each discipline have specialized formal educations, training and experience in examining soils. Approximately AUD$5 million of analytical instrumentation allows CAFSS to provide a wide range of services.

To date, CAFSS has helped investigate more than 90 criminal and environmental forensic cases — including one involving the kidnapping and rape of a nine-year-old child. Similarities between soil found on shoes from the suspect’s house and samples from the crime scenes involved helped crack the case.

CAFSS was also crucial in solving the case of the illegal clearance and theft of AUD$11 million worth of tree ferns from national parks in Victoria, Australia.

Criminal investigations

The aim of forensic soil analysis is to associate a soil sample taken from an item, such as shoes, clothing, shovel or vehicle, with a specific location.

To achieve this, the methods of analyses must be able to discriminate between soil samples from different locations. These methods must be standardized, inexpensive, accurate and applicable to small and large samples alike.

A developing area of soil forensics is its use in intelligence work. A person, for example, may claim to have never been to a particular location, but is then found with soils from that area, thus linking the individual to a geographic location.

CAFSS undertakes research and case work for the police — including the Australian Federal Police and state police departments — and forensic laboratories across the country.

Using state-of-the-art soil technology, CAFSS collects and analyzes soil evidence and disseminates their findings concerning suspects, witnesses, victims or crimes scences, which is critical to investigators.

CAFSS staff members are also regularly subpoenaed to testify in court. As a result, CAFSS is faced with responsibility as well as increased scrutiny and accountability.

In this regard, CAFSS has recently developed its Guidelines for Conducting Criminal and Environmental Soil Forensic Investigations. The guidelines are designed to provide a more systematic approach and use of appropriate standard methods for sampling, characterizing and examining soils for forensic comparisons.

They also assist CAFSS in its mission by ensuring efficiency and accountability in the proper handling, storage and tracking of soil evidence, which is essential to evidence collection and ultimate prosecution.

Evidentiary value

These days, soil forensics, as a newly developed discipline of soil science, has matured to the extent that well-defined questions and successful crime scene investigations are being addressed in increasingly refined ways.

In fact, five cases in Australia have been solved with no forensic work done because detectives have simply mentioned to the suspect or legal teams that soil samples have been or will be compared and investigated by forensic soil scientists.

Soil materials are powerful pieces of contact trace evidence, and may even be considered as approaching the ideal contact trace for six reasons:

1. Soil is highly individualistic in that there are thousands upon thousands of different soil types, enabling forensic examiners to distinguish between soil samples.
2. Soil has a strong capacity to transfer and stick especially the fine clay- and silt-size fractions.
3. Unlike the more obvious bright transfer colours of blood, lipstick smears and paint, soil is nearly invisible. Fine soil materials, especially when they impregnate vehicle carpeting, shoes or clothing, are often not visible to the naked eye; a suspect will often make little effort to remove them.
4. Soil materials are easily located and collected using hand lenses or light microscopes when inspecting crime scenes or examining items of physical evidence.
5. Soil materials are easily described and characterized by colour and by using various analytical methods such as x-ray diffraction (mineralogy) and spectroscopy (chemistry).
6. In Australia, a national computerized database of soil profile data and maps can be readily produced by police or soil scientists by downloading information directly from the Internet via the Australian Soil Resources Information System database.

Future

The type of soil information used to help police in forensic investigations may involve the application of accurate soil descriptions of colour, soil maps, soil minerals, soil biology (plant roots), soil chemical and physical properties, such as pH level or soil magnetism.

The challenges of associating small amounts of soil information from one source with that from another will require new sophisticated laboratory methods, such as the analysis method created by CAFSS staff to characterize extremely small soil particles.

However, more holistic approaches are currently being adopted by also using inseparably linked forensic disciplines, including forensic geology, forensic archaeology and environmental forensics.

Dr. Rob Fitzpatrick is a certified professional soil scientist, a Professorial Fellow at Flinders University (School of Chemistry and Physical Sciences) and an associate professor within the School of Earth and Environmental Sciences at the University of Adelaide, Australia.

For more information, visit: www.clw.csiro.au/cafss/