Fingerprints, Impression and Trace Evidence
What this domain tests
This domain covers latent print detection and development, impression evidence, trace evidence collection, and ACE-V documentation.
Core rules and concepts
- Print types: latent (invisible), patent (visible, such as blood), and plastic (impressed in soft material).
- Sequence: photograph before treatment; use powder on non-porous dry surfaces; cyanoacrylate fuming for non-porous items; ninhydrin, DFO, or 1,2-indanedione for porous paper; physical developer for wet or aged paper.
- Footwear and tire impressions: photograph with scale, then cast with dental stone or lift with an electrostatic lifter when appropriate.
- Trace evidence: use tape lifts, tweezers, or hand picking; package in paper; avoid cross-transfer.
- ACE-V means analysis, comparison, evaluation, and verification; document each stage.
Worked example
A latent print on a drinking glass is developed with black powder. You photograph it with a scale, lift it with tape, place it on a card, and submit it for ACE-V. Reasoning: powder makes the ridge detail visible; photographing before lifting preserves the location; verification by a second examiner strengthens the conclusion.
Traps
Powdering a wet surface; lifting before photographing; using too much powder; casting a shoe impression with the wrong water ratio; losing trace by using the same tweezers; skipping elimination prints.