Footwear Impression Evidence
Footwear Impression Evidence
This domain tests recognition, recovery, and comparison of footwear impressions - both two-dimensional residue prints and three-dimensional impressions. Questions target the recovery sequence, casting technique, and the limits of comparison language.
Recovery sequence
Photograph first, with a scale in the same plane as the impression, fill the frame, and use oblique lighting to reveal detail in dust or residue. Only then attempt recovery. Two-dimensional prints on non-porous surfaces may be lifted with gelatin or electrostatic lifters; porous surfaces call for chemical enhancement. Three-dimensional impressions in soil or snow are cast, typically with dental stone mixed to a measured consistency and poured around the impression, not directly into it.
Comparison
Examiners compare class characteristics - tread pattern, size, manufacturer/model, and general wear - and individual characteristics such as cuts, gouges, embedded debris, and distinctive wear. A conclusion of identification requires individual characteristics; class agreement alone supports only an association or inclusion.
Worked example
A partial shoe print at a door shows a herringbone tread. The suspect's shoe is the same size and pattern but shows no wear transferable to the print. The reportable conclusion: the print is consistent with the shoe's class characteristics but cannot be attributed to that shoe. Calling it a match is an error; so is an exclusion, since the print may come from another shoe of the same model.
Traps
Casting before photographing; pouring dental stone directly onto the impression and destroying detail; omitting a scale or placing it above the impression plane; flash at 90° that washes out texture; and overstating conclusions from class data alone.