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Ch. 17: Fingerprints Part 4

Ch. 17: Fingerprints Part 4. http://www.cartoonstock.com/directory/f/forensics.asp. IV. Development (enhancement) of Latent Fingerprints. A. Composition of Latent Print Residue 1. Eccrine sweat glands --Type of gland in friction ridge skin --Produce watery sweat

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Ch. 17: Fingerprints Part 4

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  1. Ch. 17: Fingerprints Part 4 http://www.cartoonstock.com/directory/f/forensics.asp

  2. IV. Development (enhancement) of Latent Fingerprints A. Composition of Latent Print Residue 1. Eccrine sweat glands --Type of gland in friction ridge skin --Produce watery sweat --This sweat = basis for latent fingerprint residue

  3. Fingerprint Techniques Manual, page6 --New Mexico Department of Health --http://dhi.health.state.nm.us/elibrary/ cchspmanual/fingerprint_manual.pdf

  4. A. Composition of Latent Print Residue (cont.) 2. Apocrine sweat glands   --Type of gland found elsewhere on body   --Produce oily sweat   --Can become part of fingerprint residue 3. Substances from the environment

  5. A. Composition of Latent Print Residue (cont.) 4. Summary = after evaporation of water, residue is ½ salt and ½ organic compounds such as amino acids, lipids, vitamins, and oils

  6. B. Three Categories of print enhancement (Physical, chemical, alternate light) 1. Physical Methods (effective on hard, nonabsorbent surfaces) a. Powder Dusting --Inorganic powders --Several colors

  7. 1. Physical Methods (continued) b. Magnetic Brush --Magna Brush --Uses special magnetic powders (colors) --Powder adheres to fatty components in residue --Gentler b/c no bristles

  8. 1. Physical Methods (continued) c. SPR = Small Particle Reagent --Spray that adheres to lipid components of residue --Useful on evidence that has been wet

  9. 2. Chemical Methods of Fingerprint Development --involves chemicals/chemical reaction

  10. a.-Silver Nitrate (AgNO3) • AgNO3 reacts with salt in residue • . . . not used often anymore . . . • Items which have been wet may be leached of their chloride and salt impressions. • Surfaces that have high chloride or salt compounds coating their surfaces or imbedded in them will produce unacceptable background staining.

  11. b. Iodine fuming • used for prints on porous paper • iodine sublimes with heat and reacts with fatty oils in print residue • forms visible yellowish-brown print • BUT . . .very short lived, so must photograph immediately

  12. c. Ninhydrin • Used for prints on paper and porous surfaces • Biochemical reagent that reacts with amino acids • Makes a bluish-purple image **Development time can take up to 10 days**

  13. d. Super glue (Cyanoacrylate) • Used for prints on non-porous surfaces • Super glue induced to fume in enclosed chamber • Cyanoacrylate ester reacts with print residue to make white permanent impression • Can then treat with powders or fluorescent dye

  14. e. Physical developer (PD) • Photographic-type process that deposit silver onto print (dark gray reaction) • Reacts with lipids or water-insoluble components • Good for items exposed to water

  15. 3. Special Illumination • --Oblique lighting, bright-white light sources, UV lights can be used solo or in combo with other methods • --allow for view of ridge detail, especially to then be photographed

  16. Specials … • How would you get prints out of blood? • Most techniques do NOT interfere with the collection & processing of DNA • Best to use STICKY SIDE POWDER – composed of lycopodium powder mixed with detergents & water

  17. Overall Process of FP Examiner: Analysis Comparison Evaluation Verification When collecting & processing evidence: -photograph always -collected printed objects 1st -use least destructive techniques -techniques depend on surface textures (porous vs. nonporous)

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