Why Do Forensic Scientists Use Soil Analysis?

Forensic scientists find telling clues to a crime within soil.

Soil analysis and forensics have been in use for more than 100 years. Soil is analyzed to determine the location of a criminal act, such as murder, or the path of transportation, such as a route used by drug dealers. By examining microscopic and chemical elements of soil, forensic scientists can narrow down a location to specific areas.

Soil Analysis and Forensics

The benefits of soil analysis were first postulated by Sir Conan Doyle in his "Sherlock Holmes" series in the late 19th century. However, the use of soil analysis in forensics did not begin officially until some years later, specifically 1904. Since then, soil evidence and analysis have been used extensively by forensic scientists and in criminal investigations.

Sampling

Soil analysis begins by taking a sampling. Soil is hugely diverse in its characteristics. By examining components of soil;, such as minerals, oxides, microorganisms, fossils and other types of organic matter, a forensic scientist can determine the geography of the sample. Samples may be taken from anywhere. In the case of a vehicle, soil samples come from the interior and exterior of the front bumper and grill, wheel wells and tires, engine compartment, rock panels, tops of mufflers, the interior of the vehicle (including the trunk), rear bumper (interior and exterior), trim on the body and the windshield, and, finally, swabbing the exterior of the vehicle.

Unusual Matter

Aside from the elements that make up soil, forensic scientists also look for anomalies, such as glass fragments or uncharacteristic fibers. Something as simple as a piece of thread can link a suspect to the site of a possible struggle. In some cases, the unusual matter may actually be the soil.

Screening

Soil analysis is comparative in nature. Soil from one location is compared with that of another. The actual makeup of the soil and the size of the particles, among other characteristics, are compared relative to another sample.

For example, Interpol relates a case where forensic scientists used soil analysis to reveal a murderer in Japan. A man was found dead on Mount Fuji, where a particular type of lava occurs. This lava has certain particulates and occurs nowhere else in the world. The same soil was found in the car of the murder victim's wife and on her shoes. By screening the soil where the wife lives, forensic scientists determined that the soil there lacked any of the same lava-based particulates. This was enough to get a conviction.

Primary Minerals

The relative composition of the soil relative to the minerals it holds may also be used in forensic soil analysis. For example, Interpol tells of a rape case in New Jersey that was solved using soil recovered from the shoes and pant legs of the suspect. The soil, although typical for New Jersey, contained large amounts of coal fragments lacking minerals that would be present in naturally coal-rich soil. The detectives were able to trace the rape to an abandoned lot where coal had burned regularly in the past.

Likewise, the presence of certain types of clay, the amount of minerals and relative size can be used to determine a location as specific as a section of a county. The presence and extent of clay mineral deposits, as well as the presence of organic matter in the soil, can pinpoint a location.

References

• Interpol: Forensic Examination of Soil Evidence