What Are Fingerprints?

• Friction ridges are found on skin of

– palms of hands

– palmar aspect of fingers

– soles of feet

– solar aspect of toes

• Designed by nature for firmer grip and

resistance to slippage

Skin Structure

• Epidermis = outer, surface layer of skin

• Dermis = inner layer of skin

• Dermal papillae = area between dermis

and epidermis

• Papillary pattern determines the form

and pattern of the friction ridges on

skin surface

Cross-section of human skin

Uses of Fingerprints

Can be used to identify:

• Suspects

• Victims

• Other persons who touched a surface

• A corpse

• People who might use aliases to disguise their illegal intent

First Principal: Fingerprints are

Unique

• Millions of prints taken over 90 years

• No two fingers have yet been found to have

identical ridge characteristics (minutiae)

• Identical (monozygous) twins

– have same DNA

– have different fingerprints

Second Principal: Fingerprints

are Unchanged through Life

• Friction ridge pattern of skin develops in

utero (before birth)

• Pattern remains unchanged throughout life

Do fingerprints remain

unchanged?

• Impossible to do, but many have tried

– John Dillinger-corrosive acid

• To change the pattern requires

obliteration of the dermal papillae (1- 2

mm deep)

Left middle fingerprint

Permanent scar

Third Principal: General Patterns

allow systematic classification

• The 3 basic fingerprint patterns

1. Loops (60-65%)

2. Whorls (30-35%)

3. Arches (5%)

Three Categories of

Fingerprints

• Plastic prints – Created when the fingers touch against some

material such as putty

• Patent or visible prints – Formed when the fingers are contaminated with

such things as ink or blood and touch a clean surface

• Latent/invisible prints – Left on a surface from the small amounts of body

oil and perspiration that are normally found on friction ridges

– visible

Fingerprint patterns

Loops

• Must have:

– One or more ridges that enter from one

side of the print, re-curve, and exit from

the same side

– One Delta

– One Core

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Ulnar Loops

Opens toward the

little finger

Print from the right hand

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Radial Loops

Opens toward

the thumb

Print from the right hand bsapp.com

Arches • Formed by ridges entering from

one side of the print, rising

slightly and exiting on the

opposite side.

• No Deltas

• No Cores

Arch patterns

Whorls

• One or more cores

• At least two deltas

Whorl patterns

Plain Whorl

• At least one ridge makes complete

circuit

– Can be spiral, oval, or any variant of a

circle

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Plain Whorl

• Two Deltas

• One Core

• Symmetry

Central Pocket Loop

• Two Deltas

• One Core

• Lacks Symmetry

• A delta is often near the core

Double Loop

Two loops combined into one

fingerprint

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Double Loop

• Two Deltas

• Two Cores

• Appears to

have an “S” in the print

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Accidental

• All other

prints that

cannot be

classified in

the other

groups

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Fingerprint ridge characteristics

Loop pattern

Fingerprint ridge characteristics

Individual vs. Class Evidence

Class Evidence

• General pattern

(L.A.W)

Individual Evidence

• Minutiae patterns

• Scars, etc.