Processing and Recovery of Fingerprint Evidence

Types of Fingerprint evidence that can be found: Plastic – Fingerprints impressed in a soft substance such as wax, soap, putty, or dust. Visible – Fingerprints left by fingers that have been coated with a colored substance such as ink or blood. Latent – “Hidden” fingerprints that must be developed.

Latent Fingerprints Latent prints contain: Perspiration (secreted by the pores in the friction ridges) Moisture Sodium chloride Amino acids Other substances Body oils (acquired by contact with other parts of the body, such as the face or hair) Dead epidermal cells and foreign substances

Finding Prints Points of entrance and exit Objects or surfaces that may have been disturbed during the crime Avoid handling objects if possible Handle only by surfaces that are unreceptive to fingerprints Fingerprint expert gets priority on objects such as firearms and documents Correctly label and transport to prevent destruction

Flashlight and Magnifying Glass used to find fingerprints Place flashlight at acute angle Laser can be used RUVIS – Reflected Ultraviolet Imaging System – ultraviolet rays can reveal fingerprints that were previously undetected

Processing Prints Plastic or Visible print should be photographed first. Latent print should be developed as little as possible, then photographed. Print is then taken to lab (on object if possible)

Methods for Developing Latent Prints Nonporous surface Powder (dust with brush or magnetic powder) Cyanoacrylate fuming (super glue) Vapor adheres to latent residue upon condensing, building up and hardening the ridges. Follow by dusting or adding chemical dyes Photograph before lifting Use adhesive tape to lift print

Porous Surfaces (paper, cardboard, unpainted wood) Ninhydrin – reacts with amino acids Sprayed on – amino acids turn purple Silver Nitrate – reacts with sodium chloride and light Paper is soaked in AgNO3 – turns brown Iodine – combines with oils in print Turns red-purple. Fades over time, so print must be photographed immediately Prints on dead bodies can be developed with cyanoacrylate

Procedure for Lifting Fingerprints with Iodine Place piece of paper containing fingerprint into ziploc bag without opening. Place one small scoop of iodine crystals into the bag and immediately zip the bag. Gently shake the bag for 5-10 minutes, or until the print is visible. Remove paper from bag and immediately zip bag. Prevent any iodine from escaping the bag as a solid or vapor.

Procedure for Lifting Fingerprints with Iodine (continued) Compare fingerprint with known fingerprints. Match minutiae (minimum 10 points)