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Why Fingerprints?

Why Fingerprints?. Fingerprints are the most recognizable physical evidence for the general public. When clear fingerprints are found at a crime scene they are the premier evidence which will help to identify the person who left them. Fingerprints are individual characteristics.

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Why Fingerprints?

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  1. Why Fingerprints? • Fingerprints are the most recognizable physical evidence for the general public. • When clear fingerprints are found at a crime scene they are the premier evidence which will help to identify the person who left them. • Fingerprints are individual characteristics. • In 1990 the FBI introduces the AFIS system which allows for nationwide searches on its 10-finger cards.

  2. Characteristics of Fingerprints • Fingerprints are impressions produced by the friction ridges of the fingers.

  3. Characteristics of Fingerprints

  4. Characteristics of Fingerprints

  5. Characteristics of Fingerprints • Fingerprints have the following forms: • Visible • Plastic • Latent • Latent prints are: • normally found at crime scenes. • more easily developed on smooth nonporous surfaces. • difficult to develop on porous surfaces. • Fingerprints come in three different patterns: • Arches • Loops • Whorls

  6. Arches

  7. Loops

  8. Loop Patterns

  9. Whorls

  10. Developing Latent PrintsPowders • Used on smooth nonporous surfaces. • Choice of color depends on color of surface. • White or gray on dark surfaces. • Black on light-colored surfaces. • Powder applied by camel’s hair brush or magnetic brushes.

  11. Developing Latent Prints Chemical Means • Used on absorbent materials such as paper, wood and cloth. • Three major chemicals are ninhydrin, iodine and silver nitrate.

  12. Developing Latent Prints Chemical Means • Ninhydrin • Ninhydrin reacts with the amino acids deposited in the perspiration from the sweat glands of the fingers. • Ninhydrin is considered a carcinogen, making its use problematic.

  13. Developing Latent Prints Chemical Means • Iodine • One of the oldest methods of developing a latent print. • Iodine vapor is absorbed by the oily residues deposited in fingerprints. • Iodine-visualized prints disappear with time.

  14. Developing Latent Prints Chemical Means • A silver nitrate solution will develop latent prints by reacting with sodium chloride found in the sweat residue deposited in fingerprints. • The resultant silver chloride, when exposed to light, will form a black outline of the ridges.

  15. Developing Latent Prints“Super Glue Fuming” • Cyanoacrylate glue molecules adhere to body oils • Usually used with powders • Advantage: print impression are good. • Disadvantage: fumes are toxic. • Heat accelerates this process. • Best used smooth and rough non-porous, plastic/packaging, soft vinyl (PVC), rubber, leather, metal and waxy surfaces.

  16. Developing Latent PrintsInduced Luminescence • Laser light will induce luminescence in finger prints and can be recorded photographically. • Alternative Light Sources may also be used.

  17. Developing Latent PrintsVacuum Metal Deposition • First developed in Europe in 1976. • Until recently, the only VMD in North America could be found at the Royal Canadian Mounted Police. • Most sensitive method for developing latent prints on non-porous surfaces.

  18. Developing Latent PrintsVacuum Metal Deposition • How VMD works: • Evidence is placed in a vacuum chamber. • The chamber is brought to a vacuum and a few milligrams of gold is evaporated to form a very thin layer of metal on the surface. • The gold film is uniformly distributed across the surface of the evidence and penetrates the fingerprint deposit.

  19. Developing Latent PrintsVacuum Metal Deposition • How VMD works: • Zinc is then evaporated in the chamber. • The zinc binds to the gold but does not penetrate the fingerprint deposit. • The ridges appear transparent, whereas the furrows and the background are dark.

  20. Developing Latent PrintsVacuum Metal Deposition • Zinc is then evaporated in the chamber. • The zinc binds to the gold but does not penetrate the fingerprint deposit. • The ridges appear transparent, whereas the furrows and the background are dark.

  21. Developing Latent PrintsVacuum Metal Deposition • VMD is best used on: • Most smooth, non-porous surfaces • Plastic packaging materials • Smooth leather surfaces • Photographic negatives and prints • Plastic moldings • Glass • Smooth paper • Some smooth fabrics

  22. Developing Latent PrintsVacuum Metal Deposition • Advantages • Extreme sensitivity. • Can reveal old prints and prints exposed to water. • Can detect monolayers of fat on smooth surfaces. • Can sometimes reveal fingerprint detail when all other techniques have failed. • Disadvantages • Initial cost of equipment ($32-100K). • Zinc will eventually oxidize; photos must be taken immediately.

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