The forensic comparison of trace amounts of soil on a pyjama top with hypersulphidic subaqueous soil from a river as evidence in a homicide cold case

In a cold case investigation of a 1983 homicide, trace amounts of soil were identified on a 10-year-old victim’s pyjama top. Swatch samples were cut from the pyjama top, specifically the hem, to determine the provenance of this questioned soil. A comparative study was undertaken of the questioned soil with control soils from the Onkaparinga estuary using morphological observations with the naked eye and scanning electron microscopy (SEM), chemistry, traditional laboratory X-ray diffraction (XRD) and synchrotron ľ-XRD. Synchrotron ľ-XRD with high intensity X-rays provided greater sensitivity and resolution than the laboratory XRD source to identify pyrite and clay minerals on the pyjama top. SEM confirmed that these mineral particles are deeply impregnated in gaps between fibres of the fabric, which likely originated under water with force being applied on the pyjama top—implying the victim was pushed into the mud. This is substantiated from transference shaking experiments where mineral particles are dominantly located on the surface of the fabric. The questioned soil samples have a moderately strong degree of comparability with the control hypersulphidic subaqueous soils containing pyrite in the Onkaparinga River estuary—providing evidence that the soils have similar origins. The accused was found guilty by a Supreme Court judge of murder.