Transcript document
Latent Fingerprint Accidental or by chance impressions of the friction ridges of the fingers and palms, which are reserved reproduction and are evidentially value left or transferred into the receiving surface by a transferring medium. Latent prints are: Produced by the natural oil or from perspiration secreted through the pores of the friction skin Found frequently on smooth surfaces as a result of exudation of the watery substances, which now come out from the pores on the surface of the skin. Not normally readily visible to the naked eye. May also be produced by fingers which have been in contact with foreign matters such as blood, paint, grease and semi-solid substance. Categories of Latent Prints Invisible prints Visible Prints Marks made by perspiration and other substances on the skin surface, which require the application of a latent fingerprint technique to develop so that it may be examined and photographed Prints that can be seen without any enhancement Plastic Impression Molds formed by friction ridges generally caused by touching semi-solid substance, which is capable of retaining a three-dimensional representation of the friction ridges Types of Latent Fingerprint Tape/Lifters Black and white rubber fingerprint lifters Ideal for prints on curved surfaces Protected by .005 celluloid covers Black and white opaque fingerprint lifters Transparent fingerprint lifters Good contrasting background but must be reversed through photography Continuous roll, cellophane or polyethylene base Black and white hinge lifters Pre-assembled to eliminate cutting and handling Types of Fingerprint Powder Velvet Powder Standard fingerprint powder Magnetic Powder Ferrous powder applied with a magic wand Should not be used on ferrous objects Fluorescent and Phosphorescent Powder Used like ordinary powders but fluoresce brightly under ultraviolet illumination Colors of Fingerprint Powder Commonly Used Black Powder May be applied on light colored object Contrast well Gray/ Silver Powder May be used for glass objects, metal surface which have been polished to mirror-like finish that appear black in black and white photography White Powder May be used in nickel, unpainted tins, silver and highly polished colored metal object Should be used on mirrors Latent Fingerprint Techniques Powder or Dusting Technique Physical Technique Application of powder using fingerprint brush to have maximum photographic contrast with the the background being dusted Developing reagent like iodine adheres or stick to the sweat in latent prints (sublimation) Chemical Technique When the developing reagent comes in contact with the chemical composition of the sweat, another chemical composition is formed or a chemical reaction takes place Chemical Technique Ninhydrin Dependent upon traces of amino acid that gives blue-violet color (bluish-purple to almost red) when treated with ninhydrin Silver Nitrate Dependent upon the reaction of sodium and potassium chloride present in the perspiration with silver nitrate to form silver chloride and sodium nitrate that appear reddish-brown against the background Iodine, Ninhydrin and Silver Nitrate are generally applied in looking for fresh prints on paper or cardboard.