Latent Print Development and Examination
The Latent Print domain tests development chemistry by substrate, sequential processing order, documentation, and the ACE-V examination of friction ridge impressions.
Substrate-driven processing
- Non-porous (glass, metal, polished plastic): powder, cyanoacrylate fuming, small particle reagent, luminescent dyes and RUVIS.
- Porous (paper, cardboard, raw wood): 1,2-indanedione, DFO, ninhydrin, and physical developer for wet or aged items.
- Blood-contaminated prints: amido black or leucocrystal violet first, then protein stains.
- Sequence from least destructive to most destructive; visual inspection and oblique or alternate light precede all chemistry, and powder should not precede amino acid reagents on paper.
ACE-V
- Analysis assesses clarity, quantity, level 1 (pattern), 2 (minutiae) and 3 (pores, edge shape) detail, distortion and substrate effects.
- Comparison, evaluation and independent verification follow; blind verification is preferred.
- Conclusions are identification, exclusion, or inconclusive/no value, phrased in standards-based language.
Worked example. A print on a glossy magazine cover is semi-porous. Visual and oblique light examination comes first, then cyanoacrylate fuming with a dye stain for the coated side, while the untreated paper edge is reserved for indanedione. Photograph the developed print with a scale before lifting.
Traps that cost marks
- Powdering paper before amino acid reagents, destroying or masking ridge detail.
- Lifting before photography.
- Equating ridge count with sufficiency; clarity and distortion matter more.
- Ignoring substrate texture or curvature as a source of distortion.
- Reporting a match without documented analysis and verification.