Describe the different steps in the process that is used to compare pattern evidence. Explain the importance of each step.
Answer
i) The first step is to ensure that the proper specimens are being compared, that is a positive to a positive and a negative to a negative. For example, an indentation of a shoe at the crime scene is a negative impression. A cast of the indentation is a positive impression. The cast can then be compared to the shoe pattern itself (positive-to-positive). An imprint of the shoe pattern on a tile floor at the crime scene is a negative impression. A tape lift of the imprint is also a negative impression. Thus a tape lift could be compared to an inked shoe pattern (negative-to-negative).
ii) The second step is to ensure proper orientation of the impressions being compared. With footwear, the left and right foot impressions must be carefully noted on the lifts or casts to eliminate any possible confusion. Once the orientations for the Q and K impressions are established, the positive-to-positive or negative-to-negative impressions can be compared.
iii) The third step is the comparison of class characteristics, such as brand, size, shape and general pattern features. These must match prior to proceeding to step four. If only the class characteristics can be compared. A conclusion of "the Q pattern is consistent with that of the K pattern" can only be stated for the match.
iv) The fourth step is to compare individual characteristics such as those created by random and accidental cuts, tears, abrasions etc. If a sufficient number of individual features are found to match in both the Q and K specimens, and there are no unexplained differences in the patterns, then the examiner can conclude that the Q and K patterns came from the same source (a positive identification).
2. Describe the principle ways of collecting and preserving imprint and indentation patterns.
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