The Use of Digital Microscopy for the Forensic Examination of Footwear

Abstract

During the forensic examination of footwear evidence, test impressions are taken from shoes and compared with footwear marks from crime scenes. Currently, enlargement of footwear marks is only conducted if there is visible detail at 1:1. This thesis uses a Keyence VHX 7000 digital microscope to examine 3 pairs of Nike Air Max 270 shoes for detail that could be used for comparison. Test impressions were taken to see if Schallamach were visible between replicates. Results indicate that when there is no visible detail in static test impressions at a 1:1 scale, the use of magnification at 50x and 200x exposes detail that can also be identified in three replicated impressions and the outsole that created them. Without conducting a deeper examination with the use of a Keyence VHX 7000 digital microscope, this level of detail would not have been located. In practice, this could mean that there have been instances that detail has been missed during the forensic examination of crime, and therefore, exposes a potential risk of missed convictions.

Due to a lack of research exploring footwear evidence, the understanding that static test impressions are more favourable for recording fine detail is based on anecdotal
means, and not through published validation. By experimenting with and discontinuing the use of dynamic test impressions (oil and magna with black and red fluorescent powder and Printscan) within this thesis as there was no recorded detail within these test impression methods, this thesis provides data to support the anecdotal practice.

X2 tests were conducted to enable a deeper understanding of the relationship between the detail seen in footwear test impressions and the outsole by using correspondence scores. Ultimately, there is a significant relationship supporting the view that if a 1:1 footwear impression does not show detail, that this does not mean that there is no detail to be seen; the introduction of microscopy may be required to reveal it.

Moreover, the works within this thesis have revealed that poor quality test impressions require a higher level of magnification (200x) than those that are considered a good quality, with only requiring a magnification of 50x. A finding like this can support the forensic examiner when attempting to examine a challenging print. Although further work has been suggested to continuously improve this novel method, the author proposes that with the suggested work, this method has the potential to be used by forensic science providers.