Advantages of Mineral Grain Analysis in Forensic Soil Investigations: Case Studies from North Carolina, United States

Chemical analysis of soils as trace evidence can be valuable in determining potential for a physical link between a suspect and a crime scene. However, traditional methods often involve bulk dissolution of soils, which can cause issues with use of the methods and interpretation of data. The soil present on footwear, car floormats, etc., is often in quantities which can be too small for dissolution protocol to be viable. Additionally, soil on evidence such as footwear can come from multiple sources, and dissolving the sample homogenizes those sources producing data that may not yield meaningful interpretations. Electron microprobe analysis provides a method for individually analyzing mineral grains from samples, allowing for a smaller sample size to be used and the possibility of separating out grains from different sources based on chemical composition. This method has been successfully used in first degree murder cases from North Carolina, and could prove a valuable addition to forensic geologists' arsenal of analytical techniques.