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

5.  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

8. Loops

9. Loop Patterns

11. Whorls

16. Developing Latent Prints Powders  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.

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

18. 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.

19. 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.

20. 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.

23. 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.

24. Developing Latent Prints Induced Luminescence  Laser light will induce luminescence in finger prints and can be recorded photographically.  Alternative Light Sources may also be used.

25. Developing Latent Prints Vacuum 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.

26. Developing Latent Prints Vacuum 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.

27. Developing Latent Prints Vacuum 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.

28. Developing Latent Prints Vacuum 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.

29. Developing Latent Prints Vacuum 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

30. Developing Latent Prints Vacuum 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.