Forensic Soil Analysis Using the Electron Microprobe: The Markice-Bowling Case

Abstract

Electron probe micro-analysis (EPMA) is a standard analytical tool for geologists, metallurgists and material scientists. EPMA can provide very high spatial resolution, quantitative chemical analyses of a wide variety of materials. Used predominantly for rock and mineral analyses by geologists, the electron probe is gaining traction as an invaluable tool to measure metal compositions, degradation of electrical components and in some special cases, biological samples. In this work, we present a case where EPMA analysis was used in the forensic analysis of soil.Soil is formally defined as a mixture of rock and sediment that has been modified by physical and chemical interaction with organic material and rainwater over a period of time [1]. Soil formation is strongly related to local geology such that a mass of soil will consist of varying proportions of minerals that are usually derived from the underlying geologic unit, mixed with organic matter. Due to geological variations, the individual components themselves will also vary in composition across several different chemical systems such as major elements, minor elements, trace elements, and isotopes. The combinations of all these variations mean that the mineral components of a soil sample from any given location may have a distinctive composition that can be used to differentiate it from soil in other locations. By establishing the compositional differences between soil from various locations, it then becomes possible to determine if soil in trace evidence, such as on a suspect's shoe, is consistent with the crime scene and not from other alibi locations. In addition to natural variations in soil composition, materials may be brought into an area for the purposes of construction or erosion abatement and will have different mineral compositions from those of the native soil. These natural and induced variations should provide ample differences that can be exploited to identify a location through careful analysis of the soil mineral composition. Key to this study was the ability to perform precise, quantitative chemical analyses on very small sample quantities.The case, NC v. Jordan Peterson, examined forensic soil evidence collected from a pair of shoes and sweat pants worn by the suspect and from two dental stone casts of foot prints from the crime scene (referred to in the Forensic report and here after as samples 6A and 7A; [2,3]). All samples contained white mica. The suspect declined to provide potential locations for exclusion samples. To demonstrate the variability of mica compositions in a larger context, material containing mica representative of local Piedmont rock types was collected for inclusion in the chemical analysis. Three "Index Sample" sites were selected and sampled based on rock type and ease of access.Two different procedures were used to mount samples for EPMA; polished acrylic mounts and double sticky-sided carbon tape adhered to a microscope slide. Polished acrylic mounts were prepared for the index samples due to the abundance of mica. ...

Examining the transfer of soils to clothing materials: Implications for forensic investigations

“…Forensic soil analysis has long been implemented in multiple high profile criminal justice cases, from murders such as the Soham Murders, UK, to international justice cases such as the Bosnian genocide (Ruffell, 2006;Kukes, 2015). In forensic scenarios, soils are frequently recovered from artefacts and clothing that may be used to link or eliminate potential scenes of crime from suspects and victims (Petraco et al, 2008;Swindles and Ruffell, 2009;Fitzpatrick and Raven, 2012;Fitzpatrick et al, 2014;Singletary and Hanna, 2018). The assumption of being able to utilise such evidence is underpinned by Locard's Exchange Principle (1930) which states that wherever there is contact between two objects, a 'mutual exchange of matter' will occur.…”

“…Therefore, soils are extremely useful trace evidence, and can be subjected to multiple analyses of both the organic and inorganic fractions. From the inorganic soil fraction, colour (Junger, 1996;Sugita and Marumo, 1996), particle size distribution (Dudley, 1976;Blott et al, 2004;Pye and Blott., 2004), mineral composition (Graves, 1979;Ruffell and Wiltshire, 2004;Murray, 2004;Ruffell and McKinley, 2005;Petraco et al, 2008), elemental composition analysis (Petraco et al, 2008;Raut, 2012;Singletary and Hanna, 2018), particle size distribution (Sugita and Marumo, 2001) and scanning electron microscopy (Cengiz et al, 2004;Ruffell and McKinley, 2008;Pirrie, 2018) can all be used to differentiate between forensic soils. In terms of the organic fraction, soil organic matter (Melo et al, 2018), mycology (Wiltshire et al, 2014) and palynology (Mildenhall et al, 2006;Wiltshire et al, 2014;Wiltshire, 2016), can prove to be powerful tools in forensic science as no two locations' palynological profiles have yet been found to be precisely identical (Wiltshire et al, 2014).…”