Fingerprints: Methods of Detection
Crime Scene Fingerprints Visible/Patent Prints – Fingerprints made when the finger leaves a visible material Plastic Prints – Fingerprints that leave an impression on a soft material Latent Prints – Invisible fingerprints
Locating and Visualizing Prints Depend on the type of surface Hard/Nonabsorbant surfaces Glass, mirror, tile, painted wood Soft/porous surfaces Papers, cardboard, cloth RUVIS – Reflected Ultraviolet Imaging System
RUVIS UV light identifies prints on non-porous surfaces UV light absorbs print UV light is reflected back to the viewer as green light
Methods of Visualization Physical Methods Fingerprinting powder Chemical Methods Iodine fuming Ninhydrin Super glue fuming
Fingerprint Powder Powder is applied lightly with a brush Select the color of the powder that gives you the best color contrast with the surface being dusted Gray powder – aluminum dust Black powder – carbon or charcoal Fluorescent powder Powder adheres to perspiration residues or body oils left on the surface Magnetic fingerprinting powder
Iodine Fuming Oldest chemical method Procedure Not permanent Put fingerprint surface in a chamber with solid iodine crystals Heat solid iodine to the vapor state Vapors fill the chamber and combine with the latent print to make it visible Not permanent PHOTOGRAPH print to keep a permanent record!
Ninhydrin Apply to porous surfaces Ninhydrin attaches to amino acids present in perspiration Prints usually appear in 1-2 hours https://www.youtube.com/watch?v=NuGGQ2XK9RM
Super Glue Fuming Used on non-absorbent surfaces 98-99% cyanoacrylate ester Procedure Put super glue on a cotton ball Place cotton ball and print surface in a chamber for up to 6 hours Interacts with and adheres to the latent print making it visibly white
Preservation Once the latent print has been visualized, it must be permanently preserved for future comparison in court Photographs must be taken Preserve image Show’s location with respect to other evidential items at the crime scene
Preservation Small objects Large immovable objects Print preserved in entirety Cover print with cellophane Large immovable objects “Lift” print with tape Place tape on labeled card
Fingerprint Enhancement Lifted prints are not usually in perfect condition Digital Imaging Software can enhance fingerprints for the most accurate and comprehensive analysis Scan print into digital file Change brightness, contrast, filters Comparison function
AFIS Automated Fingerprint Identification Systems: Computer that uses automatic scanning devices to convert the image of a fingerprint into digital minutiae that contain data showing the ridges at their points of termination and the branching ridges. Position and orientation of minutiae are determined to convert the fingerprint into a geometric pattern
AFIS A set of 10 fingerprints can be searched against a file of 500,000 10-finger in 8/10 of a second Computer produces a list of prints that have a high degree of correlation Selected prints are examined by a trained fingerprints expert Any AFIS user can exchange data with any other AFIS user