An examination procedure for forensic soil analysis in trace evidence laboratories

Abstract

Currently,in Australia,the majority of forensic soil examinations are not conducted within forensic facilities but by a limited number of experienced soil scientists. The research presented in this thesis developed an examination procedure for forensic soil samples in a trace evidence laboratory utilising instrumentation commonly available in such a laboratory,including microspectrophotometry (MSP),attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FTIR) and elemental analysis using X-ray fluorescence spectroscopy (XRF),scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) or laser induced breakdown spectroscopy (LIBS). Further,a suggested soil examination protocol that integrates the skill set of crime scene examiners,trace evidence scientists and specialist geologists was established. In this study,29 soil specimens were analysed,with 12 specimens coming from six geologically similar sites in the Canberra area and the remaining 17 specimens previously collected from other sites around Australia by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and stored as part of the CSIRO National Soil Archive. The soil specimens used in this study were selected to assess the examination procedure against both soil specimens from similar geological environments (the Canberra area soils) and soil specimens from vastly different geological environments (the CSIRO soils). The 29 Australian soil samples analysed could be classified into 21 different groups based on colour analysis using MSP and L*a*b* chromaticity coordinates. Using ATR-FTIR,the organic and inorganic components of the soil sample can be readily analysed and compared,resulting in the generation of an IR spectrum of the whole soil sample. Based on this spectrum,the ATR-FTIR can be used to screen and discriminate soil samples with as little as micrograms of material. Across the 29 soil samples analysed in this way,a very high discrimination of 99.7% differentiation was achieved. A high level of discrimination of the soil sample set analysed was achieved for all the elemental techniques (92.4% discrimination for LIBS,98.5% discrimination for XRF and 99.5% discrimination for SEM/EDX). This study has demonstrated that these elemental profiling techniques can be readily applied to detect differences in the elemental compositions of soil specimens. Individually,each of the instrumental techniques demonstrated high discrimination of the soil set analysed. However,when combined,full discrimination of the soil set analysed was achieved with MSP followed by IR and then one of the elemental profiling methods. Utilising the proposed instrumental examination procedure from this study (i.e. dry sieving followed by MSP,ATR-FTIR and elemental analysis),the following is a suggested soil examination protocol that integrates the skill set of crime scene examiners,trace evidence scientists and specialist geologists to enable best practice for the triaging and examination of forensic soil samples. This protocol consists of four distinct stages,the first three of which could take place in typical forensic trace evidence laboratories: Stage 1 – Known soil sample collection and preservation by crime scene examiners. Stage 2 – Questioned soil sample collection and preservation by trace evidence chemists during the examination of items submitted for forensic analysis. Microscopic examination of the soil sample for exogenous material followed by preliminary screening of dry sieved questioned and known soil samples for differences using instrumentation currently available in trace evidence laboratories,including MSP,IR and a form of elemental analysis,either LIBS,XRF or SEM-EDX. Stage 3 – Limited identification of minerals present in soil specimens coupled with the instrumental examination procedure from Stage 2. Note that,in order to complete Stage 3,typical trace evidence analysts would require some level of specialist training with respect to basic mineralogy. Stage 4 – Geological and/or palynological examinations by a subject matter expert for casework that is complex,where provenancing is required,when the questioned sample is particularly small,or when additional instrumental expertise is required. The proposed instrumental examination procedure (dry sieving the soil sample,followed by MSP,ATR-FTIR and an elemental analysis) allows for high discrimination and differentiation of soil samples,without destructively altering the soil,thereby retaining an unadulterated soil sample for the soil scientist so they can complete their analyses. The proposed instrumental examination procedure will develop stage 2 skills and promote the value of soil examination with investigators. Validation of the proposed instrumental examination procedure is underway for implementation of the procedure in the AFP Chemical Criminalistics trace evidence laboratory. The proposed soil protocol would ensure integration of the stages undertaken by the trace evidence examiner in a forensic science laboratory and the higher-level analyses that could be performed by geological and/or palynological experts. The re-integration of soil examinations into forensic laboratories using the proposed instrumental examination procedure as part of the larger soil examination protocol will allow for the objective differentiation of soil samples in a timely and efficient manner. This would facilitate soil examinations to assist in intelligence-led policing,rather than the more typical reactive forensic analyses.

Date of Award	2014
Original language	English
Supervisor	James Robertson (Supervisor), Paul Kirkbride (Supervisor) & Christopher Lennard (Supervisor)