Footwear and Tire Impression Evidence
The Footwear domain tests recovery of two- and three-dimensional impressions, enhancement choices, casting technique, and the comparative ACE-V process that ends in a defensible conclusion.
Recovery
- Photograph first: camera back parallel to the impression surface, frame filled, scale in the same plane, plus an orientation shot.
- 2D impressions (dust, blood, residue): electrostatic dust print lifter for dry residue on hard surfaces; gel lifters for wet or bloodstained prints; amido black or leucocrystal violet for blood; powder for dry dust on smooth surfaces.
- 3D impressions (soil, sand, snow): dental stone cast mixed to a thin-cream consistency, poured from one edge with a retaining border and reinforcement; snow needs a cold-water mix or a hardening agent.
Comparison
ACE-V: analysis of suitability, comparison of class characteristics (general tread design, pattern type, approximate size), then individual characteristics (cuts, nicks, wear, embedded debris, manufacturing artefacts), then independent verification. Conclusions are identification, exclusion, or inconclusive/association.
Worked example. A partial heel print in blood on tile shows a distinctive perimeter tread and three accidental cuts. The recovered shoe shares the tread design and all three cuts in matching relative position; the conclusion is an association with that shoe. If the tread matched but wear differed sharply, the correct answer is exclusion or inconclusive, not identification.
Traps that cost marks
- Converting impression length directly into a shoe size; lasts vary and size is not a measurement.
- Naming a brand or model from a pattern without a reference standard.
- Lifting before photographing.
- Forgetting that an outsole impresses as a mirror image, so orientation must be checked.
- Comparing a left shoe to a right-foot impression.
- Mixing dental stone too wet, losing fine detail.