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

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

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.

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

Dusting for Prints

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.

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.

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.

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.

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

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.

Watch the video and then answer the questions. Video Link: Courtesy of The Science Spothttp:// 1. What is the name of the activator used during the process? A. Hot PrintsB. Hot StuffC. Hot Shot 2. During fuming the super glue heats up and attaches to _____ _____ in the fingerprint. A. SkinB. Amino AcidsC. Valleys 3. The evidence is placed in a super glue _____ to develop the prints. A. ChamberB. TubeC. Slide 4. What color is the fingerprint after it develops? A. RedB. WhiteC. Yellow

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