2 Wednesday - 10/19/11 Objective: Do Now: Today: To describe the characteristics of fingerprintsDo Now:Are fingerprints considered class or individual evidence?Today:Last H-option PresentationFingerprinting
3 Thursday – 10/20/11 Objective: Do Now: Today: 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 NotesTen cards
5 WHAT ARE FINGERPRINTS? Hands, feet have unique pattern of skin ridges Skin is coated with mix of sweat and oilsAny time you touch a surface, a trace amount of sweat/oil is left behind
6 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 patternsTwins do NOT have identical printsGenetics does NOT determine your exact prints
7 HISTORY2000 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 person1879: Alphonse Bertillon, clerk at a police records office in Paris, uses fingerprints to identify a repeat- offender criminal
8 Types of FingerprintsPatent 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
15 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.)
16 Characteristics of Fingerprints (Book pg 137 – you need to see pictures!)Arches (5%)Plain and TentedWhorls (30%)Plain, Central pocket loop, double loop, accidentalLoops (65%)Delta—a triangular region near a loopCore—the center of a loop or whorlPURPOSE: categories provide quick way to eliminate suspects. They DO NOT give an individualized identification of one person.
37 IAFISIntegrated 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 databaseMatches take hours, not seconds!
38 Detection of Latent Prints Dusting with powdersSpraying/applying ninhydrinExposing to cyanoacrylate fumes (superglue)Spray or dip in silver nitrateExpose to iodine fumes
39 DUSTING FOR PRINTSFine dusts (often charcoal) stick to the sweat and oils on printsWorks best on smooth, nonporous surfaces (plastic, smooth metal, polished wood, glass)Colored dusts provide better contrast depending on surfaceExcess dust blown awayFingerprint is then photographedThen “lifted” with tape and placed on a fingerprint collection card
40 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)
41 Iodine fumingGets 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 colorIt fades quickly unless sprayed with a starch solutionNot used much anymore – more toxic, less sensitive than other methods
42 Iodine fingerprint (photograph it or spray it with starch!)
44 Cyanoacrylate (superglue) Gets prints that are on plastic, metal, or glassItem 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)
46 Ninhydrin Best for getting prints off of paper Paper is sprayed with a solution of ninhydrin in acetone or alcoholNinhydrin reacts with amino acids (proteins) in sweat and becomes purple-blueTakes up to 24 hours for prints to appear; ninhydrin is toxic and flammable
47 Silver nitrateGets prints from paper, wood, Styrofoam (better at detecting faint prints than almost any other method)Object sprayed or dipped in AgNO3Chloride from salt in sweat reacts to become silver chloride (AgCl), a white compoundSilver chloride is black or reddish-brown under UV lightAgNO3 + NaCl AgCl + NaNO3Permanently damages the material—used as a last resort if other methods fail
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