Bloody Partial Heel Print on Ceramic Tile
A 42-year-old man is found deceased in a kitchen with a ceramic tile floor. Near the body, a dried bloody footwear impression shows only the heel and posterior midfoot; it is 7.0 cm long and 8.5 cm wide. The outsole pattern is a fine herringbone with a distinctly worn lateral heel edge. The print crosses two grout lines and the heel area is smeared, indicating the foot rotated while depositing the blood. No full-length impression is present. Thirty-six hours later, investigators seize a size 10.5 athletic shoe from a suspect; the outsole has a herringbone pattern and a small pebble embedded in the lateral heel. The suspect says he was in the kitchen the previous week but not on the day of the homicide. A test impression in blood on similar tile is requested. The laboratory must decide whether to report an identification, an association, or no conclusion, and how to address the pebble and the wear.
1. What conclusion categories are defensible from this partial print, and what facts would move you from one category to another?
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Defensible conclusions run from exclusion through inconclusive and association to identification, depending on laboratory terminology. Here the class characteristics - herringbone outsole, approximate size, and heel width - are consistent, so exclusion is not supported. Identification is not supported by a partial, rotated heel print alone. The worn lateral heel is a wear pattern that could be shared by many shoes of the same model and use; it is not unique unless the pattern is highly distinctive and reproduced in detail. The pebble is an accidental characteristic, but its evidential value depends on three things: a corresponding void or notch in the questioned print, proof or a reasonable basis to conclude the pebble was present at deposition, and reproduction in a test impression. Because the pebble could have been picked up after the homicide and no documentation shows it earlier, it cannot carry an identification by itself. The proper conclusion is likely inconclusive or a limited association: the suspect shoe is consistent with and cannot be excluded as a source, but the evidence is insufficient for identification. If the print shows a clear pebble void matching the suspect pebble in size, shape, and position, and test impressions reproduce it, the conclusion could rise to identification under a validated SOP, but the persistence issue must be stated.
2. Describe the test impressions and documentation you would perform before finalizing the comparison.
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First document the questioned print in place with a scale and oblique lighting; record the tile grout lines, smear direction, and blood matrix. Then examine the suspect shoe: photograph and measure the pebble, its location, the wear facet, and any blood. Make test impressions in blood on similar ceramic tile, using the heel area at several pressures and rotation angles to mimic the smear. Make impressions with the pebble in place, then remove it and repeat, so you can see what the pebble contributes. Compare class characteristics such as ridge spacing, herringbone angle, and heel shape, and accidental characteristics such as the wear facet and pebble void. Use a known test print of the entire outsole to orient the partial. Test whether the pebble creates a void or an extra deposit. Document chain of custody and avoid cleaning the shoe before testing. If the questioned print lacks a pebble void but test impressions show one, that suggests the pebble was not present at deposition or that area was not printed; do not ignore it. Consider requesting other shoes owned by the suspect.
3. The defense argues that the pebble could have been picked up after the homicide and that the wear pattern is common. How do you respond in your report and testimony?
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Concede the limitation directly. The pebble is an accidental characteristic only if it was present at the time of the crime and produced a detectable feature in the print. The defense is correct that a pebble can be picked up later and that a wear pattern can be common. The examiner should not testify that the shoe made the print based on the pebble alone. Instead, explain the conditional nature: if the questioned print contains a void matching the pebble, the shoe could have made it; if not, the pebble is not probative. The report should state the conclusion category and the reasons, including the partial nature, distortion, and lack of proof of persistence. Avoid phrases such as match or unique. The proper response is to lower the conclusion to inconclusive or association and explain that the evidence supports consistency, not identification.