GEOCHEMICAL ANALYSIS OF WHITE MICA AS TRACE EVIDENCE IN MURDER INVESTIGATIONS: AN OVERVIEW

Variations in white mica composition from soil evidence can be a valuable tool when examining the possibility of a physical link between a suspect and a crime scene in North Carolina. Key to the use of this mineral group in forensic analysis is its abundance in the soil of the North Carolina Piedmont as well as the compositional variations that occur on a scale as small as a single crime scene. Analyses are done on individual white mica grains from soil evidence using the JOEL JXA-8530F Hyperprobe at Fayetteville State University. The field emission gun in this instrument allows for significantly higher resolution analysis than traditional microprobes, enabling the collection of multiple data points from each grain to better characterize the composition.

The two case studies presented were first degree murder cases tried in Wake County, NC in which expert testimony was presented to juries. In North Carolina v. Jordan Peterson, white mica from a pair of sweatpants and a pair of Nike shoes were analyzed and compared to white mica from the crime scene. White mica samples were collected from several locations representing distinct geologic units within the County; these samples were also analyzed and used for comparative purposes. The results indicated that white mica from the shoes and sweatpants were chemically consistent with mica from the crime scene, but chemically different than white mica from other locations sampled within the County. Testimony to this affect was a major factor in the jury’s conviction of the suspect.

In North Carolina v. Bradley Cooper, white mica grains from a pair of running shoes belonging to the defendant were analyzed and compared to soil evidence from: 1) the crime scene (location of the victim’s body), 2) the defendant’s residence and 3) an area the defendant was known to have traversed while wearing the shoes. White mica was identified in all samples except for the defendant’s residence. Analysis indicated that white mica from the shoes was consistent with the location where the defendant was seen wearing the shoes. This evidence did not show a physical link between the defendant and the crime scene, but did further validate the use of this technique in forensic investigations. Work is currently being done to expand the application of this technique to non-silicate minerals.