FORENSIC SOIL EXAMINATIONS IN CRIMINAL INVESTIGATIONS

Forensic soil examinations are conducted for criminal investigations, because soil can adhere to an item of evidence, such as a pair of shoes or a shovel. This can be done for either investigative and intelligence purposes to: 1) determine if two or more geologic materials originated from different sources; 2) identify an unknown material; 3) assess the geographic attribution (provenance) of geologic materials; 4) determine the origin/end-use of geologically-derived materials; and, 5) determine the significance of finding two or more geologic materials indistinguishable.

Forensic examination of geologic materials requires the identification and comparison of class characteristics. As a result, a Forensic Examiner might conclude that two samples could have originated from the same source, however other soils that share those same characteristics could also be potential sources. Only when two or more geologic materials physically fit together can it be said that they were once part of the same broken object (e.g., brick).

Here, we present two case studies where forensic soil analysis was used in criminal investigations. In 2019, a five year old Illinois resident was reported missing and a large-scale search was initiated by local law enforcement. A pair of muddy shoes was provided to the FBI for analysis in order to identify potential sources of the soil. The material on the shoes consisted of fine-grained clay-rich soil with rounded pebble-sized dolomite fragments, which are mined locally for gravel cover on dirt roads and paths. This suggested a wet muddy source just off a dolomite gravel road. Also in 2019, a New Jersey resident went missing as her Monmouth County home went up in flames. A suspect was apprehended in northern New Jersey and a pair of muddy boots was recovered for a provenance examination. The color of the soil, pollen analysis from the USGS, and the presence of ilmenite and glauconite suggested that Monmouth County was a more likely source for the soil that northern New Jersey. In both cases, discovery of clandestine burials and direct comparison to soil from the footwear confirmed the provenance determination.