Randomly Acquired Characteristics (RACs)
Definition
Post-manufacture features (cuts, gouges, embedded material, crack patterns) unique to a specific shoe sole or tyre; the highest-level individualising features in impression comparison.
- Full name
- Randomly acquired characteristics
- Origin
- Post-manufacture damage or wear
- Examples
- Cuts, gouges, embedded stones, crack patterns
- Evidentiary weight
- Highest individualising level in impression comparison
Common questions
How do RACs differ from class characteristics in a shoe or tyre comparison?+
Class characteristics, such as tread pattern or sole size, are shared by every unit from the same production run and only narrow the pool of possible sources. RACs arise from individual wear and damage after manufacture, so a matching set can point to one specific shoe or tyre.
Why do examiners need more than one RAC before individualising an impression to a specific source?+
A single small mark could arise coincidentally or be poorly reproduced in the impression. Multiple RACs in matching position, size, and orientation, considered together with the class characteristics, are what supports a source-specific conclusion.
Related terms
- Class Characteristics (Footwear)
- The manufactured outsole design features shared by all examples of a specific shoe model: tread pattern, size, shape, and logo placement.
- Dental Stone
- A gypsum-based casting material harder and finer than plaster of Paris. Preferred for forensic 3-D casts because it captures detail at the...
- ESLA (Electrostatic Dust-Print Lifter)
- A device that applies a high-voltage static field to a metallised film, attracting dust particles from a footwear impression on a hard...
- Perpendicular Camera Alignment
- The requirement that the camera lens be directly above the impression centre with the sensor plane parallel to the impression plane; prevents...
- R V. Mohan (1994) + White Burgess Langille Inman (2015)
- Canadian Supreme Court framework for forensic-expert admissibility: Mohan sets relevance + necessity + qualification + no exclusionary rule; White Burgess adds an...
- SICAR (Shoeprint Image Capture and Retrieval)
- FBI and Foster and Freeman (UK) outsole design database used for class-characteristic database searches; referenced in US, UK, Australian, and Canadian forensic...
- Snow-Print Wax
- A spray wax applied in thin coats to snow impressions before casting to provide a thermal barrier, allowing Dental Stone casting without...
- Subclass Characteristics (Footwear)
- Features shared by a subset of shoes from the same mould or production batch; may mimic individual characteristics if not properly distinguished.
- SWGTREAD
- Scientific Working Group for Shoeprint and Tire Tread Evidence; US body that developed the dominant guidelines for footwear and tyre-mark examination, class-subclass-individual...
- Tracking Evidence (TE) Database
- FBI database of tyre tread design patterns, used for class-characteristic identification in tyre-mark cases; accessible to partner agencies internationally.
- Treadmate
- RCMP database of outsole designs for footwear comparison, used by Canadian forensic laboratories and accessible to partner agencies.