IAI CSSA cheat sheet

Crime Scene Investigation: Core Principles and Procedure

• Locard's exchange principle: every contact between two objects leaves a mutual trace; the absence of transfer is itself a finding that must be explained.

• Four crime scene search patterns and their triggers: line/strip (large open outdoor areas), grid (same area searched twice at 90 degrees for thoroughness), zone/quadrant (irregular or cluttered spaces), spiral (circular or confined areas, inward or outward).

• Scene priority order: scene safety and medical aid, scene preservation and perimeter control, scene documentation, systematic search and collection, then scene release.

• Chain of custody must record each transfer with item number, collector, date/time, location, and receiving party; any gap renders the item vulnerable to admissibility challenge.

• Perimeter sizing rule: initial boundary is set larger than the apparent scene and reduced only after documentation; a log records all persons entering or leaving.

• First responder duties: render aid, secure and isolate, detain witnesses and suspects present, note original scene conditions (lights, doors, weather) before alteration.

• Photography sequence: overall, mid-range, close-up, and close-up with scale; each image logged with frame number, direction, and distance from subject.

• Sketch types: rough sketch at scene (not to scale), finished scale sketch with fixed reference points and triangulation or baseline measurements.

• Classification decision: primary scene is where the incident occurred; secondary scene is any other location where evidence or consequence is found; macroscene versus microscene refers to scale, not importance.