Footwear Impression Evidence
Footwear impressions are found at virtually every crime scene—they are often more available than fingerprints. Impressions fall into three categories: patent (visible prints in blood, mud, or dust), latent (invisible prints requiring development with electrostatic lifting or chemical enhancement), and plastic (three-dimensional impressions in soft substrates like snow, mud, or wet soil). Class characteristics include sole pattern design, size, and manufacturer—databases like SoleMate contain over 40,000 outsole designs from major shoe brands. Individual characteristics develop through wear and damage: cuts, scratches, embedded stones, and uneven wear patterns create features unique to a specific shoe. Casting three-dimensional impressions with dental stone (a gypsum-based casting material) preserves fine detail for laboratory comparison.