Likelihood of Randomly Acquired Characteristics (RACs) in Crime Scene Shoeprints

Music City Center 

Forensic shoeprint examiners have been criticized for relying on subjective rather than objective, quantitative methods to determine whether a suspect's shoe sole matches a crime scene impression. After confirming a match in pattern, size, and wear, experts assess whether randomly acquired characteristics (RACs) correspond. A correspondence of rare RACs supports the hypothesis that the two impressions originate from the same source.
This study, conducted with the Israel Police and the Center for Statistics and Applications in Forensic Evidence, examines RAC visibility in crime scene-like conditions rather than ideal lab settings. Controlled experiments with pre-selected shoes featuring numerous RACs simulated thefts, leaving impressions on various surfaces. A total of 302 shoeprints from 30 simulated crime scenes were analyzed, identifying 488 RACs.
The study assesses how RAC visibility varies by print quality and surface type and develops a probabilistic model estimating the likelihood of RACs appearing in specific locations. The collected data serve as a basis for black-box studies on examiner decision-making and for improving the reliability of RAC analysis in forensic practice.