The forensic analysis of sediments recovered from footwear

The forensic analysis of sediments recovered from footwear has the potential to yield much useful information concerning the movements of a person before, during and after a crime has taken place. Three experimental studies and a number of examples of forensic casework provide insight into the complexity of the spatial distribution of geoforensic materials on the soles of footwear and the persistence of these materials over time on the soles and uppers. These findings have implications for both the geoforensic sampling protocols and procedures for footwear submitted for analysis in a criminal investigation and also for the analysis of any materials recovered. The preservation of sediment on a shoe sole will vary, with certain areas generally retaining more sediment than others. The sequential layering of sediments that have been transferred to the shoe will be preserved in some cases and in certain areas, but generally undergoes complex mixing. Such mixing of sediment from different sources occurs both across the shoe sole and also through time. It is therefore important to be aware of these variations when taking samples for analysis if representative samples are to be taken and meaningful interpretation of any analysis derived is to be effected. Furthermore, such mixing of pre-, syn- and post-forensic event sources has implications for the appropriateness of different analytical techniques. Visual identification techniques which are able to identify where such mixing has taken place are preferred to forms of analysis that require homogenisation of the sample prior to analysis, as this reduces the possibility of false negative or positive associations when undertaking comparison of samples in a forensic context. The context within which any sampling or analysis is undertaken is crucial for a meaningful and accurate interpretation of the geoforensic evidence.