Technological innovations in the collection and analysis of three-dimensional footwear impression evidence.

Abstract

The development of digital 3D trace recovery in the fields of geology and archaeology has highlighted transferable methods that could be used for the recovery of 3D footwear impressions under the umbrella of forensic science. This project uses a portfolio of experiments and case studies to explore the veracity and application of SfM Photogrammetry (i.e., DigTrace) within forensic footwear. This portfolio-based research includes published papers integrated into conventional chapters. A method of comparing the accuracy and precision of different measurement methods is developed and introduced and gives a comparative view of multiple recovery techniques. A range of simulated crime scene and laboratory-controlled experiments have been conducted to compare different recovery methods such as casting, photography and SfM photogrammetry. These have been compared for accuracy, practicality and effectiveness. In addition, a range of common and lesser common footwear bearing substrates have been compared using SfM as well as other methods. One of the key findings shows that DigTrace SfM photogrammetry software reliably produces accurate forensic results, regardless of the camera used for initial photography and in a multitude of environments. This includes but is not limited to, soil, sand, snow, and other less obvious substrates such as food items, household items and in particular carpet. The thesis also shows that SfM photogrammetry provides a superior solution in the recovery of ‘difficult to cast’ footwear impressions. This finding allows for 3D recovery of impressions that would otherwise have only been photographed in 2D. More generally this project shows that 3D recovery is preferential to 2D and aids in the identification of individual characteristics and subsequent positive analysis. Overall, the thesis concludes that SfM photogrammetry is a viable and accurate solution for the recovery of 3D footwear impressions both as an alternative and replacement to 2D photography and conventional 3D casting. SfM 3D recovery provides increased visualisation of footwear evidence and individualising marks. Digital evidence obtained in this way integrates with the increasingly sophisticated search algorithms being used within the UK’s National Footwear Database and allows rapid file sharing, retrieval and evidence sharing. Moreover, the technique has significant cost saving in terms of time, equipment and resources. It is the author’s opinion, having consulted a wide audience of footwear examiners and crime scene employees, that this technique should, and can be, adopted quickly by forces in the UK and USA and disseminated for use.