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Methods of Detecting Fingerprints

Methods of Detecting Fingerprints. 2 Types of Crime-Scene Prints. 1. Visible Print- A fingerprint made when the finger deposits a visible material such as ink, dirt, or blood onto a surface. 2. Plastic Print- A fingerprint impression in a soft surface. Ex: Putty, Wax, Soap, or Dust.

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Methods of Detecting Fingerprints

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  1. Methods of Detecting Fingerprints

  2. 2 Types of Crime-Scene Prints • 1. Visible Print- A fingerprint made when the finger deposits a visible material such as ink, dirt, or blood onto a surface. • 2. Plastic Print- A fingerprint impression in a soft surface. • Ex: Putty, Wax, Soap, or Dust

  3. Locating Fingerprints • Visible Prints: This job is easy for the investigators. • Latent Prints- (invisible prints) • Much harder • Requires the use of techniques to make the print visible • Type of surface the print is located on determines what technique is used

  4. Latent Print Retrieval • Hard & Nonabsorbent Surfaces: Such as Glass, mirror, tile, & painted wood • Prints are developed by the application of powder or treatment with Super Glue.

  5. Soft and Porous Surfaces: such as papers, cardboard, and cloth. • Require treatment with 1 or more chemicals

  6. Dusting for Prints

  7. Developing Latent Prints • 1. Fingerprint Powders- These powders stick to perspiration residue & body oils left on a surface. • Should use a fiberglass or camel’s hair brush • Pick a color that contrasts with the surface • Fluorescent powders are also used and they show up under a UV light.

  8. 2. Iodine Fuming- A technique for visualizing latent fingerprints by exposing them to iodine vapors. • Oldest chemical method used • Iodine is a solid crystal that when heated is transformed into a vapor without passing through a liquid stage. • Sublimation: A physical change from the solid directly into the gaseous state.

  9. As the solid crystals are heated the vapors combine with parts of the latent print to make it visible. • These prints are not permanent and will begin to fade once the process has stopped. • Examiner should photograph the prints • Can also apply a 1% solution of starch in water & the print turns blue and lasts for several weeks-months.

  10. 3. Ninhydrin: A chemical reagent used to develop latent fingerprints on porous materials by reacting with amino acids in perspiration. • Sprayed onto the porous surface from an aerosol can. • Prepared by mixing the ninhydrin powder w/ a solvent such as acetone. • Forms a purple/blue color when reacting with amino acids present in trace amounts of perspiration.

  11. 4. Physical Developer- a silver nitrate- based reagent formulated to develop latent fingerprints on porous surfaces. • Very effective on porous surfaces that may have been wet at one time • Silver-nitrate reacts with salt deposits in sweat

  12. 5. Super Glue Fuming- A technique for visualizing latent fingerprints on nonporous surfaces by exposing them to cyanoacrylate vapors; named for the commercial product Super Glue. • Develops latent prints on surface such as metal, electrical tape, leather, & plastic bags • Super Glue is 98-99% cyanoacrylate ester • The chemical that interacts with & visualizes a latent fingerprint.

  13. Watch the video and then answer the questions.Video Link: http://www.youtube.com/watch?v=FkcSkADVMIMCourtesy of The Science Spot • 1. What is the name of the activator used during the process?A. Hot Prints B. Hot Stuff C. Hot Shot • 2. During fuming the super glue heats up and attaches to _____ _____ in the fingerprint.A. Skin B. Amino Acids C. Valleys • 3. The evidence is placed in a super glue _____ to develop the prints.A. Chamber B. Tube C. Slide • 4. What color is the fingerprint after it develops?A. Red B. White C. Yellow

  14. references • http://www.drakeinvestigations.com/Portals/56/Fingerprints%20for%20Forensic%20Section.jpg

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