Soil: Forensic Analysis

Abstract

Abstract Earth materials such as soils, rocks, minerals, and particles from man‐made materials such as bricks provide excellent evidence to link criminals to crime scenes. Forensic soil scientists are also using advanced automated techniques, which have the ability to acquire information from smaller samples to make soil forensics an increasingly popular tool in criminal investigations. The aim of soil forensic analysis is to associate soil, rock, or mineral samples taken from an item, such as shoes, clothing, shovel, or vehicle with a specific location. Soil materials are powerful, perhaps ideal, pieces of contact trace evidence to help in criminal investigations. Soil forensic investigations usually involve collection of one or more soil samples followed by soil characterization. Collected samples are categorized as (i) questioned soil samples whose origin is unknown or disputed (suspect or victim), (ii) control soil samples whose origin is known (crime scene), and (iii) alibi soil samples whose origin is known and that provide a measure of the distinctiveness of the questioned and control samples. Soil characterization often requires the following four‐stage approach, which combines descriptive, analytical, and spatial information: (i) Initial characterization for screening of samples involving morphological descriptions. (ii) Semi‐detailed characterization involving semi‐quantification of minerals and organic matter following sample selection and size fractionation (<50 µm). (iii) Detailed characterization and quantification of minerals and organic matter using additional analytical techniques and/or methods of sample preparation, separation, or concentration such as size or magnetic or heavy mineral fractionation. (iv) Integration and extrapolation of soil information from one scale to the next, to build a coherent model of soil information from microscopic observations to the landscape scale, which often involves soil/geological maps and geophysics. Progression of a soil forensic examination through each of the four stages will depend on the amount of sample available and the results from the early stages of the examination. The significance and relevance of established concepts and standard terminologies used in soil science and geology with practical relevance to forensic science are emphasized.