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Fingerprint Detection and Processing

Fingerprint Detection and Processing. Fingerprint 2. Fingerprints as Evidence. Three forms Visible prints Found with the naked eye Made after ridges come in contact with a colored material Plastic print Left on a soft material like putty, wax, etc. Latent

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Fingerprint Detection and Processing

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  1. Fingerprint Detection and Processing Fingerprint 2

  2. Fingerprints as Evidence • Three forms • Visible prints • Found with the naked eye • Made after ridges come in contact with a colored material • Plastic print • Left on a soft material like putty, wax, etc. • Latent • Left after body perspiration or oils touch the surface of an object

  3. Processing Techniques • Fingerprint “lifting” consists of many techniques from the simple to the very complex • Technique used is dependent upon the type of material, quality of print and environment • Many techniques (esp. chemical) are temporary and must be photographed immediately

  4. Processing Techniques • Powder • Among the most common and easiest to use • Powders come in dark and light forms • Correct choice depends on the color of the surface • Uses dusting brush • Lightest touch must be applied • Powder evenly spread over the print • Powder will stick to the oils in the print • Print is lifted with ordinary cellophane tape

  5. Processing Techniques • Iodine Fuming • Oldest chemical technique • Iodine crystals sublimate in air • Will react with either the perspiration or fatty oils in the print (still not clear which is correct) • Very effective especially if heated inside a fuming chamber • Must be photographed immediately since prints will fade rapidly • Can be “fixed” with a 1% starch solution A laboratory-grade fuming chamber Note: Iodine fumes are poisonous and should not be inhaled

  6. Processing Techniques • Ninhydrin • A chemical that reacts with amino acids in perspiration • Reveals purple/blue prints • Usually sprayed on the object • Development may take several hours • Technique has been used successfully on 15 year old fingerprints • Very good for lifting prints from paper, cardboard Note: Ninhydrin solutions are mildly poisonous and exposure should be minimized.

  7. Processing Techniques • Cyanoacrylate • Commercial super glue • Will produce fumes if heated or dripped on to a cotton ball treated with sodium hydroxide • Fumes will “stick” to latent prints revealing a white colored print • Very popular due to ease of obtaining materials • Especially useful on metals, leather, electrical tape, plastic bags Note: Super glue fumes are poisonous and flammable in high concentrations.

  8. Processing Techniques • Other techniques • Additional chemical techniques exist for almost every kind of surface • Use of polarized light, UV fluorescence • Lasers

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