Partial Grease Print on a Glass Door
At a commercial burglary, a latent footwear impression in grease was found on the lower pane of a glass door. A gelatin lift shows a partial outsole: the heel and midfoot are clear, but the toe is absent. The outsole has a zigzag tread and a circular logo area. Using the heel-to-midfoot length, the original examiner estimates a men's size 10.5-11. A suspect is arrested with size 9 athletic shoes that have a different zigzag pattern and no circular logo. The suspect's shoes are new and show minimal wear. The laboratory must decide whether the class differences justify an exclusion, whether the size estimate is reliable from a partial print, and whether the logo area is a class characteristic. The door glass is flat, but the print is slightly smeared at the heel.
1. Can the suspect be excluded? Explain your reasoning.
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Exclusion can be based on class characteristics when the questioned print is of sufficient quality and shows a different outsole design. The suspect shoe has a different zigzag pattern and no circular logo; if the questioned lift clearly shows a circular logo area and a different zigzag geometry, the suspect shoe cannot have made the print. That is a valid exclusion, provided the examiner confirms the differences are real and not artifacts of distortion, smearing, or the gelatin lift. The size estimate from a partial heel-to-midfoot print is weaker: it depends on outsole dimensions, manufacturing variation, wear, and distortion, and marked size is not the same as outsole length. Thus size alone should not be the basis for exclusion or inclusion. The pattern and logo differences are the stronger basis. The report should state the exclusion is based on class characteristics, not on the size estimate. Also request the suspect's other shoes.
2. How should the size estimate be treated in the report?
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Report the size estimate only as an approximate investigative range, not as a conclusion. Explain that a partial heel-to-midfoot length cannot reliably establish full outsole length or marked size; different manufacturers use different lasts and sizing, and wear, matrix, and smearing affect dimensions. Use a standardized measurement method and state the measurement uncertainty. If the pattern comparison already excludes the suspect, the size estimate is moot and should not be used to bolster the exclusion. If the pattern were consistent, the size estimate still could not individualize or exclude without a test impression. Avoid converting outsole length to a precise shoe size in the conclusion. Document the measurement on the lift and any test impressions used for calibration.
3. What if the suspect's shoe had the same zigzag pattern but no logo, and the print's logo area was smeared?
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If the logo area were smeared, the absence of a logo in the suspect shoe would not be a reliable difference; the examiner could not use it to exclude. The zigzag pattern comparison would then control. If the pattern is the same, class characteristics are consistent, and the examiner must examine wear and accidental characteristics. A conclusion of inconclusive or association would be appropriate; identification would require distinctive individual characteristics. The size difference would still be a weak point, not a basis for exclusion. The examiner should test whether the suspect shoe can produce the questioned pattern under similar conditions and should not overstate the significance of a partial print.