Crime Scene Investigation: Scene Integrity, Documentation, and Evidence Handling
Crime Scene Investigation: Scene Integrity, Documentation, and Evidence Handling
This domain tests how a crime scene analyst establishes control, documents conditions, and preserves evidence so that laboratory results and reconstructions remain defensible. Expect questions on first-responder priorities, contamination control, search and documentation methods, packaging, chain of custody, and the reasoning behind each decision.
Core rules and concepts
- First-responder priorities are preserve life, secure the scene, preserve evidence, and maintain safety; then notify investigators. Do not smoke, eat, or use scene facilities, and log every person who enters.
- Establish inner and outer perimeters, a command post, and a one-way entry/exit path. Wear task-appropriate PPE and change gloves between evidence items to prevent transfer.
- Document before you move: contemporaneous notes, photo log, overall/midrange/close-up photographs with and without a scale, and a sketch measured from fixed datums using baseline or triangulation, not pacing.
- Select a search pattern suited to the scene: line/strip, grid, zone, spiral, or wheel. Mark and number evidence before collection.
- Package biological evidence in breathable paper and air-dry it; place sharp items in rigid containers; collect control/reference samples; record chain of custody with date, time, name, purpose, and seal initials.
- Know legal authority: consent, warrant, exigency, and plain view; stay within scope.
Worked example
A burglary scene has a bloodstain on a windowsill and a muddy footprint below it. Reasoning: photograph overall, midrange, and close-up with scale before moving anything; triangulate the stain and print to two fixed points; swab the stain after air-drying and collect an adjacent unstained control swab; cast or photograph the footprint with scale; package each item separately and document each transfer. The control sample reveals background DNA, air-drying limits degradation, and separate packaging prevents cross-transfer.
Traps that cost marks
Moving evidence before photography; sealing damp blood in plastic; omitting a control sample; using plastic for biological evidence; incomplete chain-of-custody entries; describing a pattern without testing; and recording “evidence collected” without item numbers.