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:• 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

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

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

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

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

WHAT TYPE IS THIS?

A)LatentB)PlasticC)Patent

WHAT TYPE IS THIS?


WHAT TYPE IS THIS?


WHAT TYPE IS THIS?


AFTER DUSTING FOR PRINTS…

WHAT TYPE IS THIS?


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.)

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 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.

PLAIN ARCH- No core- No delta- 4% of

population

TENTED ARCH- No core- Presence of a

DELTA is what makes it “tented”

- 1% of population

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

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

DOUBLE LOOP WHORL- Contains 2

loops (so 2 cores)

- 2 deltas- 4% of

population

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

LOOP- Has core, but

the core has no complete circles around it

- 1 delta- 65% of

population

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?

























8)WHAT TYPE?- How many cores












RIDGE COUNT- Way to help

individualize prints

- Imagine a line from core to edge of delta

- Count how many ridges are crossed

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)

Comparison of Minutiae

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!

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

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

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)

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

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

After Image Adjustment…

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)

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

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

Documents

FINGERPRINTS