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Importance of Fingerprints: Identification, Presence, Interviews, Retrieval

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  1. IMPORTANCE OF FINGERPRINTS • Positive identification of the offender • Prove presence at the scene • Victim, witnesses, and suspect • Frequently found at scenes • Useful in interviews of suspects • Relatively easy to process with limited equipment • Do not change from womb to grave

  2. CLASSIFICATION • Formula (alpha-numeric) given to all 10 fingers on a fingerprint card based on • Pattern type • Ridge count • Ridge tracing • i.e. 15 O 9 R OOM 17 M 17 U OOO • Pattern areas (loops/whorls) consist of cores, deltas, and ridges • Filing system for retrieval

  3. FINGERPRINT IDENTIFICATION • Friction ridges on fingers, thumbs, palms • Feet included (toes and bottom of feet) • Compare with lifts at scene and 10 print cards

  4. FINGERPRINT IDENTIFICATION • Points are identified – no set number to make ID • Bifurcation – ridge forks becomes two or more • Islands – bifurcates then forks into ridge • Ending ridges and dots – just that • Short ridge – no longer than width of corresponding ridges • Divergence – spreading apart of two parallel ridges

  5. VISIBLE IMPRESSIONS • Visible – finger coated with foreign material transferred to a clean object • “Dust” prints coated in dust • “Patent” prints coated in oil, blood, etc. • Visible w/o processing or light • Difficult to lift – photograph, electrostatic dust lifter

  6. PLASTIC IMPRESSIONS • Result of fingers pressed into a soft surface, putty, wet paint, soap, grease, recently painted surfaces, adhesive tape, etc. • Difficult to lift, photograph and lift by microsil, dental stone, other molding type material

  7. LATENT IMPRESSIONS • Reproduction of friction ridges transferred to any surface touched • 98% water; and other acids, fats/oils, and salts • Hidden, need to be developed to discover • Powders and/or chemicals • Oblique lighting can sometimes help but not always the case – processing is best

  8. CONDITIONS THAT AFFECT LATENT IMPRESSIONS • Manner it was transferred (gloves, etc.) • Nature and quality of substance • Weather conditions • Physical or occupational defects of person • Condensation and heat

  9. POWDER PROCESSING FOR LATENT IMPRESSIONS • Primarily used on non-porous surfaces • If blood, hair, or other items adheres to the object, collect the item and submit to the lab • Black or gray powders preferred • If item is wet allow to dry naturally then apply powders – do not use heat sources • If too much powder used, lift the excess powder and lightly reapply then lift

  10. APPLICATION OF POWDER • Use powder sparingly – lightly distribute the powder across the print until the ridge details become visible • Use short quick strokes or twirl • Lightly brush away excess powder – don’t blow on the print • Ready to lift and/or photograph the print

  11. LIFTING THE PRINT • Enough lifting tape to cover the print • Press sticky side over the prints and smooth out to prevent air bubbles • Gently peel from one end, place on a card • Put ID data on card • Location of offense, date, case nr, offense, lifter’s name, good description of where the lift was obtained

  12. CYANOACRYLATE PROCESSING • Non-porous (hard) surfaces • Fuming chamber (fish tank/aquarium) • 3-4 drops “super glue” on tinfoil • 1/2 drop of sodium hydroxide to glue • cup warmer inside • Heat lamp outside • Fumes adhere to prints then harden into a white color – dust and lift – can be done several times VENTILATE

  13. CHEMICAL PROCESSING • Three primary chemicals: • Iodine – fats/oils • Ninhydrin – acids • Silver nitrate – salts • Can use all three on porous items but in the above order I-N-S • Need to photograph to record/capture • Caution – chemicals can cause injury and respiratory distress - ventilate

  14. IODINE PROCESSING • Iodine crystals when exposed to slight heat will vaporize producing violet fumes which adhere to fats/oils • Fuming gun, chamber with crystals, plastic bag with crystals (shake and bake) • Prints appear yellowish/brown; photograph when appear as they will fade over time

  15. NINHYDRIN • Dye that reacts to amino acids • Aerosol cans preferred • May cause inks to run – test similar item • Spray object thoroughly – beginning after one hour to 24 hours purple prints appear • Photograph with green filter before fading • Heat (iron with steam over the object) will speed up the process

  16. SILVER NITRATE • Crystals mixed with alcohol or water • Reacts to salts when immersed and blotted dry • Appear reddish brown when exposed to light and item will turned black quickly • Remove from light as soon as prints appear • Photograph quickly and store in dark area

  17. OTHER CHEMICALS • Sticky-side powder for adhesive tapes • Gentian violet for adhesive tapes • Amido black to enhance blood prints • Small particle regent for wet surfaces • Smoke technique - camphor • Silver plating

  18. LASERS AND ALTERNATE LIGHT SOURCES • Two different things • Use either before any other methods attempted • Fluorescent powders may be used • Special eyewear or flashlight lens needed to visualize the wave lengths and results (also to protect the eyes from injury)

  19. AFIS • Automated Fingerprint Identification System – computer scans the print comparing it to the data base • Class B misdemeanors and above • No palms or little fingers (#5 and #10) in TX • Takes time to enter – examiner must identify the points prior to entry • Once entered scans continuously – may take years to get result as suspect was not previously arrested

  20. TEN PRINTS PREPARATION • FBI/DPS cards • Visually inspect for problems • Disabilities – try best as possible • fresh cuts – allow to heal first • excessive perspiration – dry hands • Ink plate, printers ink, cardholder, roller • Thin coating of ink

  21. TEN PRINT PROCEDURES • Roll thumbs to center of body • Roll fingers from center of body • Roll all of them from edge to edge • Try to get the tip to below the first joint • Then all four fingers simultaneously and thumbs (this verifies correct order of individual prints)

  22. PALM PRINT PROCEDURES • DPS/FBI/Local palm cards • Use roller to ink entire palm to wrist and edges of palm • Use an aerosol can or cut piece of cardboard tubing • Roll palm onto card over the tubing/can • Many times palms are found more often at scenes than fingers – examiners love palms

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