What Are Fingerprints? - kentchemistry.com€¦ · Three Categories of Fingerprints •Plastic...

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

bsapp.com

bsapp.com

bsapp.com

Ulnar Loops

Opens toward the

little finger

Print from the right hand

bsapp.com

bsapp.com

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

bsapp.com

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

bsapp.com

Double Loop

• Two Deltas

• Two Cores

• Appears to

have an “S” in the print

bsapp.com

Accidental

• All other

prints that

cannot be

classified in

the other

groups

bsapp.com

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.