Legal medicine: acari trace evidence as forensicmarkers, when associated with crime scenes, clothed and concealed cadavers

Abstract

The structure and nature of fabrics makes them one of the most valuable tools in forensic investigations of crime scenes. Fabrics are widely used by humans, and are commonly found in households, vehicles, offices and hospitals, in the form of clothing, or as part of the surrounding furniture. Because of their structure, they are able to retain associative traces from different origins. During a crime, the individuals involved are most often dressed, and come into contact with each other. The interaction between the participants in a crime and the crime scene and/or victim, leads to an exchange of traces, following Lockard’s exchange principle. The recognition, recovery and analysis of trace evidence - particularly Acari - from clothing, are fundamental to an accurate interpretation of clues provided by these traces. The retrieval of mite evidence from scenes of crimes has yet to be fully exploited by forensic investigators. This is principally due to the technical difficulty of recovering the mites, as well as an absence of experimental data and established protocols. To address this, here we aimed to assess the performance of commercially available forensic tapes at lifting mites from clothing. Amongst the tested tapes, we found that the J-Lar tapes performed best in a mite-recovery assay. In addition, we found that the negative-phototropic characteristics of common household mites could be exploited to drive greater numbers of mites onto the adhesive tapes and gels. Moreover, for best forensic practice, mites should be collected from the clothes as soon as possible, to diminish the time that has elapsed before lifting of the mites. We also investigated the effect of concealment of dead bodies using blankets, to understand the process of decomposition in relation to the possible preservation of mite traces from before death. The associative traces can be exploited as markers of crime scene location and as indicators of movements of cadavers after death. Mites found on a decomposing body may be useful in the estimations of time elapsed since death. Adequate knowledge of the mites biology such as habitats, lifecycle and populations dynamics, are beneficial to the assessment of time of colonisation by these mites or their carrier arthropods. Mites have proven their ability as associative markers in a forensic case study due to their environmental specificity, as a result of their sensitivity to subtle environmental changes. Our findings will be useful to forensic investigators with an interest in the use of trace evidence of acarological origin to draw inference.