Fingerprinting Techniques
Latent prints – invisible Use – 1. high-intensity UV light 2. dusting – finely ground powders stick to fingerprint residues, lifted with tape, attached to labeled card – best on fresh prints
On nonporous substances 1. Cyanoacrylate fuming (super glue) - reacts with proteins and fatty acids in print when heated - item suspended in enclosed fuming chamber w/ warmed water - glue placed in small container inside chamber & heated - fumes react with print, print whitish color
2. Silver Nitrate (AgNo3) solution - reacts with salts in sweat in print forming silver chloride (AgCl2) – appears black in UV light
On Porous surfaces Ninhydrin - reacts with amino acids in print – turns purple - spray or dip item in ninhydrin – 48 hours to develop (faster if heated)
2. Diazofluoren (DFO) - paper dipped in DFO for 10 sec, dry, repeat - reacts with amino acids - visible under blue-green light
On NonMetal surfaces Vacuum metal deposition - chamber evaporates gold & zinc - gold attracted to thin layer of tissues left by print, zinc condenses on gold coating and b/t ridges
Fingerprint Database Prints – photographed, scanned, digitized - for comparisons FBI – Integrated Automated Fingerprint Identification System (IAFIS)