Latent Print Examination
Latent Print Examination
This domain tests the friction-ridge examination process and the chemistry used to make latent prints visible. Questions target ACE-V, suitability decisions, and reagent choice by surface type.
ACE-V
Analysis examines the latent for clarity, distortion, pressure, substrate, and development history, and decides whether it is of value. Comparison looks at the known print in the same sequence, from Level 1 ridge flow to Level 2 minutiae (endings, bifurcations) and Level 3 detail (pores, ridge edges, incipient ridges). Evaluation states a conclusion - identification, exclusion, or inconclusive. Verification is an independent re-examination by another qualified examiner, ideally blind to the first conclusion.
Development
Non-porous surfaces: powders (magnetic, fluorescent), cyanoacrylate fuming, vacuum metal deposition. Porous surfaces: amino-acid reagents such as ninhydrin and DFO, and physical developer for lipid residue or aged and wetted conditions. Blood impressions: amido black, leucocrystal violet, or luminol for latent blood. Sequence reagents from least to most destructive: optical/ALS first, then powders, then chemicals.
Worked example
A latent on a glossy magazine cover, previously handled and stored damp. Analysis notes the print is faint and the substrate porous with background interference; the examiner documents limited value before any comparison. Processing would use DFO, then ninhydrin, with physical developer as a later option. If ridge detail is insufficient for Level 2 comparison, the correct conclusion is "no value," not "inconclusive" forced after a comparison.
Traps
Comparing before assessing suitability; skipping independent verification; mixing reagent sequences; and overstating identification from partial, distorted, or smudged detail.