Footwear and Tire Track Examination
This domain tests the candidate's ability to preserve, enhance, document, and compare footwear and tire impression evidence, and to state conclusions within the discipline's limits. Expect questions on 2D versus 3D impressions, enhancement and lifting, dental stone casting, tire nomenclature, ACE-V, and the line between class and individual characteristics.
Core rules
- Class characteristics-tread design, size, manufacturing mold-narrow a source to a group. Individual characteristics-cuts, nicks, wear, embedded debris-are required for an identification.
- 2D residue or dust impressions: photograph with a scale under oblique lighting, then lift with an electrostatic dust print lifter or gelatin lifter; document each step.
- 3D impressions: photograph first, then cast with dental stone mixed to a smooth consistency, poured gently from an edge; reinforce and label the cast with case data and orientation.
- Tire tracks: record track width, wheelbase, tread design, and any visible tire size or DOT markings; compare to suspect tires and the vehicle.
- ACE-V conclusions are identification, exclusion, or inconclusive; verification must be independent.
Worked example
A dusty partial shoe impression on tile shows a herringbone tread consistent with a suspect's shoe size. The examiner photographs it with an ABFO scale, lifts it electrostatically, and compares. The suspect outsole has a distinctive cut across two lugs, and that feature appears in the lift in the same shape and position. The conclusion is identification-not because the pattern matches, but because the accidental characteristic aligns. Without the cut, the correct conclusion would be inconclusive, since class characteristics alone cannot identify.
Traps
- Calling a class-characteristic match an identification.
- Omitting a scale or orientation from photographs.
- Casting with stone that is too wet or too thin, losing fine detail.
- Confusing track width with tread width on tire questions.
- Failing to document the enhancement and lifting sequence.