Triangular Cut in a Dust Print on a Vehicle Hood
At a residential burglary, the suspect climbed onto the hood of a parked car to reach a second-story window. An electrostatic dust print lifter recovered a partial footwear impression from the hood: 24 cm long, with three parallel ridges in the forefoot and a small triangular defect in the heel. The hood is curved and the lift shows compression distortion at the toe. A suspect is arrested wearing size 10 athletic shoes with the same three-ridge pattern and a triangular cut in the heel. The shoes are a common model sold nationally. The suspect says he bought them two weeks after the burglary. The laboratory has the lift, the shoes, and access to a similar vehicle hood for test impressions. The key question is whether the triangular cut can support an identification or only a class association, and what steps are needed to evaluate persistence and distortion.
1. Assess whether the triangular cut is an individual characteristic and whether it can support identification.
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A cut in the outsole is an accidental characteristic and can be individualizing if it is distinctive, persistent, and reproduced in the questioned print. Here the cut is a small triangular defect and the shoe is a common national model; a single small cut is not automatically unique. The questioned lift is partial, distorted by the curved hood, and only 24 cm long; the defect is in the heel, which is present, so a comparison is possible. The critical question is whether the same defect shape, size, orientation, and position are present in the lift and whether test impressions on a similar hood reproduce them. The suspect says he bought the shoes two weeks after the burglary, so the examiner must consider that the cut may postdate the crime. If the questioned print shows the defect, then the shoe that made the print had a similar defect at the time, but that does not prove the suspect's shoe is that shoe unless the combination is sufficiently distinctive. The defensible conclusion is likely association or inconclusive rather than identification, unless the defect plus wear pattern is highly distinctive and the test impression reproduces it exactly under blind verification.
2. What test impressions and documentation are needed to evaluate distortion and the cut?
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Make test impressions with the suspect shoe on a similar curved vehicle hood, using a dust medium and the same electrostatic lifting method, at several pressures and angles. Photograph the lift and the shoe with scale; measure the triangular defect (side lengths, orientation, distance from heel edge) and compare to the questioned print. Examine the shoe for wear facets and other defects; compare ridge spacing and pattern. Use a second examiner for blind verification. Document the distortion at the toe and avoid comparing areas that are stretched. Make test impressions with the shoe in the same orientation as the print. If possible, create a 3D model or use photogrammetry to account for curvature. Also examine the suspect's other shoes and any shoes he owned at the time. The goal is to determine whether the cut is reproduced consistently, not merely whether a cut exists.
3. How should the examiner address the suspect's claim that he bought the shoes after the burglary?
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The purchase date claim must be investigated, not accepted or rejected by the examiner. If records verify purchase after the burglary, the shoes could not have been worn at the burglary unless the suspect had identical shoes earlier or the records are wrong. If the questioned print contains the triangular defect, then either the suspect had access to those shoes earlier, another shoe with a similar defect made the print, or the defect is not as distinctive as it appears. The examiner should report the comparison result and the limitation that the cut's age is unknown. It is for the trier of fact to resolve the conflicting accounts. Do not use the purchase claim to explain away a matching defect, and do not overstate the match. If the defect is not reproduced in test impressions, the claim is irrelevant to the comparison.