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FINGERPRINTS

FINGERPRINTS. Wednesday - 10/19/11. Objective: To describe the characteristics of fingerprints Do Now: Are fingerprints considered class or individual evidence? Today: Last H-option Presentation Fingerprinting. Thursday – 10 / 20 / 11. Objective:

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FINGERPRINTS

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  1. FINGERPRINTS

  2. Wednesday - 10/19/11 • Objective: • To describe the characteristics of fingerprints • Do Now: • Are fingerprints considered class or individual evidence? • Today: • Last H-option Presentation • Fingerprinting

  3. Thursday – 10/20/11 • Objective: • To describe the characteristics of fingerprints. • Do Now: • Read “Unaltered Identity” on p. 132 of text book. Answer question: • Can fingerprints be altered? Explain. • Today: • Fingerprinting Notes • Ten cards

  4. WHAT ARE FINGERPRINTS? Hands, feet have unique pattern of skin ridges Skin is coated with mix of sweat and oils Any time you touch a surface, a trace amount of sweat/oil is left behind

  5. HOW DO THEY FORM? Form on a fetus in the womb The “basal layer” of skin grows faster than the epidermis and the dermis, making it wrinkle in random patterns Twins do NOT have identical prints Genetics does NOT determine your exact prints

  6. HISTORY • 2000 BC: Ancient China & Babylon—fingerprints on clay tablets and official documents (used for ID…? We don’t know.) • 1788: Johann Mayer observes that fingerprints are unique to each person • 1879: Alphonse Bertillon, clerk at a police records office in Paris, uses fingerprints to identify a repeat-offender criminal

  7. Types of Fingerprints • Patent Prints: visible prints (left because someone’s hand had blood, ink, etc. on it) • Latent Prints: hidden prints that become visible only when fingerprint powder or other special techniques are used. Composed of sweat and body oils. • Plastic Prints: fingerprint indentations left in a soft material such as clay or wax

  8. WHAT TYPE IS THIS? Latent Plastic Patent

  9. WHAT TYPE IS THIS? Latent Plastic Patent

  10. WHAT TYPE IS THIS? Latent Plastic Patent

  11. WHAT TYPE IS THIS? Latent Plastic Patent

  12. AFTER DUSTING FOR PRINTS…

  13. WHAT TYPE IS THIS? Latent Plastic Patent

  14. Reliability of Fingerprints • UNIQUE: No two identical fingerprints have ever been found. Remain same for entire life. • ALTERATION: Fingerprints grow back. (Story of John Dillinger, a famous gangster.) Scars don’t cover the whole print. • MISTAKES: Human error is the cause of fingerprint ID errors. (Case of Brandon Mayfield/Madrid bombing.)

  15. Characteristics of Fingerprints (Book pg 137 – you need to see pictures!) • Arches (5%) • Plain and Tented • Whorls (30%) • Plain, Central pocket loop, double loop, accidental • Loops (65%) Delta—a triangular region near a loop Core—the center of a loop or whorl PURPOSE: categories provide quick way to eliminate suspects. They DO NOT give an individualized identification of one person.

  16. PLAIN ARCH No core No delta 4% of population

  17. TENTED ARCH No core Presence of a DELTA is what makes it “tented” 1% of population

  18. PLAIN WHORL Has core – ridges go in complete circle around it 2 deltas; a line drawn between deltas will cut at least one of the circles around core 24% of population

  19. CENTRAL POCKET LOOP WHORL Core has ridges in complete circle 2 deltas Line between the deltas DOES NOT cross circles around core 2% of population

  20. DOUBLE LOOP WHORL Contains 2 loops (so 2 cores) 2 deltas 4% of population

  21. ACCIDENTAL WHORL Has 2 or more deltas Combines 2 or more other patterns (loops, whorls, arches) but is not a tented arch 0.01% of population

  22. LOOP Has core, but the core has no complete circles around it 1 delta 65% of population

  23. 1) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  24. 2) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  25. 3) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  26. 4) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  27. 5) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  28. 6) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  29. 7) WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  30. 8)WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  31. 9)WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  32. 10)WHAT TYPE? How many cores does it have, if any? How many deltas does it have, if any? Does a line between deltas cross core circles?

  33. RIDGE COUNT Way to help individualize prints Imagine a line from core to edge of delta Count how many ridges are crossed

  34. MINUTIAE This is where it gets real, folks! Primary means of individualizing prints Every print has about 150 minutiae Need 8-15 for “match” (basis of computer matches)

  35. Comparison of Minutiae

  36. IAFIS • Integrated Automatic Fingerprint Identification System (was “AFIS” before going international and is often still called AFIS) • Computerized system that uses ridge counts and types/locations of minutiae to match fingerprints to the 50 million in the database • Matches take hours, not seconds!

  37. Detection of Latent Prints • Dusting with powders • Spraying/applying ninhydrin • Exposing to cyanoacrylate fumes (superglue) • Spray or dip in silver nitrate • Expose to iodine fumes

  38. DUSTING FOR PRINTS • Fine dusts (often charcoal) stick to the sweat and oils on prints • Works best on smooth, nonporous surfaces (plastic, smooth metal, polished wood, glass) • Colored dusts provide better contrast depending on surface • Excess dust blown away • Fingerprint is then photographed • Then “lifted” with tape and placed on a fingerprint collection card

  39. Dusting - disadvantages • Messy; prints can be smeared by brush (magnetic dust and magnetic dust remover helps in some situations; fluorescent dusts and UV lamps help) • Doesn’t work on rough or porous surfaces (unfinished wood; paper; Styrofoam; leather) • Not as sensitive as other techniques (which means that some prints may be too faint to appear from dusting)

  40. Iodine fuming • Gets prints from paper, cardboard, unpainted/unfinished wood (porous surfaces) • Solid iodine is heated in a vapor tent, producing iodine vapors (sublimation) • Iodine crystallizes on prints, forming a brownish color • It fades quickly unless sprayed with a starch solution • Not used much anymore – more toxic, less sensitive than other methods

  41. Iodine fingerprint (photograph it or spray it with starch!)

  42. After Image Adjustment…

  43. Cyanoacrylate (superglue) • Gets prints that are on plastic, metal, or glass • Item is placed in a “vapor tent” (enclosed area to contain fumes). Superglue is heated to create fumes. Can take hours. • Reacts with amino acids & water and becomes a white solid (harder to see than other types)

  44. Ninhydrin • Best for getting prints off of paper • Paper is sprayed with a solution of ninhydrin in acetone or alcohol • Ninhydrin reacts with amino acids (proteins) in sweat and becomes purple-blue • Takes up to 24 hours for prints to appear; ninhydrin is toxic and flammable

  45. Silver nitrate • Gets prints from paper, wood, Styrofoam (better at detecting faint prints than almost any other method) • Object sprayed or dipped in AgNO3 • Chloride from salt in sweat reacts to become silver chloride (AgCl), a white compound • Silver chloride is black or reddish-brown under UV light • AgNO3 + NaCl AgCl + NaNO3 • Permanently damages the material—used as a last resort if other methods fail

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