Chapter 4 - Fingerprints

“Fingerprints cannot lie, but liars can make fingerprints.” --- unknown

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What is a fingerprint?• An imprint made by ridge patterns on the tip

of a finger.• Also used to describe the characteristic

pattern of DNA fragments.

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Why are fingerprints useful?Properties that make a fingerprint useful for ID: It’s unique characteristic ridges which make them

individual evidence. It’s consistency over a person’s lifetime. It remains

unchanged during an individual’s lifetime.The systematic classification is used for fingertips

based on their general characteristic ridge patterns.

DactyloscopyThe Study of Fingerprints

History from 1850 to 1900

William Herschel—required Indians to put their fingerprints on contracts, and used fingerprints as a means of identifying prisoners

Henry Faulds—claimed that fingerprints did not change over time and that they could be classified for identification

Alphonse Bertillon—proposed body measurements as a means of identification; termed anthropometry

Francis Galton—developed a primary classification scheme based on loops, arches, and whorls

Edward Richard Henry—in collaboration with Galton, instituted a numerical classification system

Juan Vucetich—developed a fingerprint classification system based on Galton’s that is used in Spanish-speaking countries

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Recording and classifying prints Rolling inked prints

3 Basic patterns - Loops, whorls, arches

Ridge characteristics – Minutiae (very small)

Primary identification number

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Lifting prints

Black, white, and fluorescent powder

Chemicals—ninhydrin, iodine, silver nitrate, cyanoacrylate

Other types of prints

Palm, lip, teeth, eye, ear, voice, shoeprints, and footprints

Collection and Classification of Prints

Ridge Characteristics

Minutiae—characteristics of ridge patterns

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Fingerprint Minutiae

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LOOP

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WHORL ARCH

Basic Fingerprint Patterns

ArchAn arch has friction ridges that

enter on one side of the finger and cross to the other side while rising upward in the middle. They do NOT have type lines, deltas, or cores.

Least common type (5%) and more likely found in people of African ancestry.

Types

Plain – gradual bump

Tented – much higher, pinched arch

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LoopA loop must have one or more ridges

entering from one side, curving around and exiting from the same side. Loops must have one delta.

Most common type (65%) and more

common in people of European background. Also, forefingers have most of the radial loops.

Types

Radial—opens toward the thumb

Ulnar—opens toward the “pinky” (little finger)

Which type of loop is this, if it is on the right hand? Left hand?

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WhorlA plain or central pocket whorl has at least

one ridge that makes a complete circuit. A double loop is made of two loops. An accidental is a pattern not covered by other categories. Whorls have at least two deltas and a core.

Found in 30% of population. People of Asian ancestry are more likely to have whorls.

TypesPlain

Central pocket

Double loop

Accidental

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Four Types of Whorls

Whorl: line drawn from delta to delta intersect circle.

Double Whorl

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Central Pocket: line drawn from delta to delta do not intersect circle.

Accidental: prints too irregular to fall into any group.

Primary Classification

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The Henry-FBI Classification System

Each finger is given a point value.

right leftRight Right Left Left Left index ring thumb middle little 16 8 4 2 1 + 1 =Right Right Right Left Leftthumb middle little index ring 16 8 4 2 1 + 1 =

Example: Whorl on your left thumb and right middle finger. 0 + 0 + 4 + 0 + 0 + 1 = 5 5 is your primary 0 + 8 + 0 + 0 + 0 + 1 = 9 9 classification

**Fingerprints are given as a fraction. Identify which fingers have whorls; each whorl has a number based on which finger it is on. Loops and arches are a “0”.

Comparison

There are no legal

requirements in the United

States on the number of

points required for a match.

Generally, criminal courts will

accept 8 to 12 points of

similarity.

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Plastic Prints• Indented of molded prints• Made by pressing a finger against a plastic like

material to form a negative impression of a fingerprint.

• Examples: putty, soap, candle wax, gum, stamps, or candy bar.

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Visible PrintsLeft by a finger that has touched colored material such as blood, paint, ink, grease, chalk, mud or sometimes even dust.

Latent PrintsLatent fingerprints are those that are not visible (essentially

invisible) to the naked eye. They are impressions caused by the transfer of oils present on the finger to the surface of an object. These prints consist of the natural secretions (body oils and perspirations) of human skin and require development by chemical or physical means for them to become visible.

Most secretions come from three glands:

Eccrine—secretes largely water, with both inorganic (ammonia, chlorides, metal ions, phosphates) and organic (amino acids, lactic acids, urea, sugars) compounds. Most important for fingerprints.

Apocrine—secretes pheromones and other organic materials.

Sebaceous—secretes fatty or greasy substances.

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Developing Latent PrintsDeveloping a print requires substances that interact with secretions, causing the print to stand out against its background.

It may be necessary to attempt more than one technique, done in a particular order so as not to destroy the print.

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Powders —(“dusting”) -- adhere to both water and fatty deposits. Choose a color to contrast with the background. Best on hard, nonabsorbent surfaces. Develop print by “lifting” with clear sticky tape.

Iodine (chemical) — fumes react with oils and fats to produce a temporary (short lasting) yellow-brown colored print. Works best on porous paper.

Ninhydrin— reacts with amino acids to produce an orange to purple color. Best with paper, tissue, clothing and other porous surfaces.

Silver nitrate & UV Light — reacts with chloride in salt to form silver chloride, a material that turns into silver oxide (gray) when exposed to light.

Porous surfaces like paper and drywall.

Cyanoacrylate—“superglue” fumes react with water and other fingerprint constituents to form a hard, whitish deposit that can be treated with powders or fluorescent dyes to make a shaper contrast for photos or lifting..

In modern labs and criminal investigations, lasers and alternative light sources are used to view latent fingerprints. These were first used by the FBI in 1978. Since lasers can damage the retina of the eye, special precautions must be taken.

Other Types of Prints

Palm—friction ridges can be identified and may be used against suspects

Lips—several common patterns; not individual.

Voice—electronic pulses measured on a spectrograph

Foot—are taken at birth as a means of identification of infants.

Size of foot and toes; not individual.

Friction ridges on the foot and toes; individual

Shoes—can be compared and identified by type of shoe, brand, size, year of purchase, and wear pattern

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Other Prints, continued

A man has been convicted of suffocating an eldery woman on the basis of earprint evidence. The assailant was caught after police matched the imprint of his ear on the victim’s window. Police believe that the thief put his ear to the window to listen for signs of anyone home.

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Earprint catches murderer

Teeth—bite marks are unique and can be used

to identify suspects. These imprints were

placed in gum and could be matched to crime

scene evidence.

Eyeprint - The blood vessel patterns in the

eye may be unique to individuals. They are

used today for various security purposes.

AFISThe Automated Fingerprint Identification System—a computer system for

storing and retrieving fingerprints

Established in the 1970s, AFIS enables law enforcement officials to:

Search large files for a set of prints taken from an individual

Compare a single print, usually a latent print developed from a crime scene

By the 1990s, most large jurisdictions had their own system in place. The problem: A person’s fingerprints may be in one AFIS database but not in others.

IAFIS—the FBI’s Integrated Automated Fingerprint Identification System, which is a national database of all 10-print cards from all over the country

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Biometrics

Use of some type of body metrics for the purpose of identification. (The Bertillon system may actually have been the first biometry system.)

Used today in conjunction with AFIS.

Examples include retinal or iris patterns, voice recognition, hand geometry.

Other functions for biometrics: can be used to control entry or access to computers or other structures; can identify a person for security purposes; can help prevent identity theft or control social services fraud.

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