An Investigation of Test Impression Methods ]to Accurately Reproduce Randomly Acquired Characteristics in Footwear Outsoles

Abstract

The Scientific Working Group for Shoeprint and Tire Tread Evidence has published standards for making test impressions of footwear and tires using various methods; however, there is little published research on documenting randomly acquired characteristics (RACs) and studies comparing methods of documenting RACs. The purpose of this research was to calculate the statistical accuracy of various test impression methods of capturing randomly acquired characteristics, (such as nicks, scuffs, and cuts). This research focused on making 2D impressions of worn work boots, and sneakers with two methods: (1) the Identicator® inkless shoe print system, and (2) Handiprint® lifting material with black fingerprinting powder. For both methods, three different mechanisms were tested: (1) Dynamic step, (2) Static step, and (3) Rolled. This project was conducted in three phases. The first consisted of documenting the shoes and making the test impressions. The second phase included documenting the RACs that were reproduced on the impressions and identifying randomly acquired characteristics on the outsole of the shoes. The third, and final phase, was comprised of the statistical analysis and interpretation of the results. The statistical analyses concluded that the two techniques with the highest percentage of RACs transferred, Technique 1- Identicator® Dynamic step, and Technique 6- Handiprint® Rolled were statistically similar. The analyses also determined that Static step impressions resulted in a substantial reduction in capture efficacy. Overall, it was shown that the mechanism used to make an impression was of greater influence than the method used.