Fingerprinting

Forensics 352

Fundamental Principles of Fingerprints

• A fingerprint is an individual characteristic.

• A fingerprint remains unchanged during an individual’s lifetime.

• Fingerprints have general characteristic ridge patterns that permit them to be systematically classified.

Anatomy of Fingerprints

• Will two people ever have the same fingerprints?– No two people have the same ridge

characteristics…even identical twins!!!• Where can ridges be found?

– Ridges can be found on you palms, feet, and lips.

Anatomy of Fingerprints

• Skin is composed of an epidermal outer layer and a dermal inner layer.

• In between the epidermis and the dermis, finger-like papillae press into the epidermis causing friction ridges.

Anatomy of Fingerprints

• When the ridges press against objects, they leave an impression.

• The impression consists of natural secretions of the sweat glands.

• The secretions are a combination of water, oils, salt, and dirt.

Fingerprint Basics

• The core is the center of a fingerprint.• A delta is triangular area found on a

fingerprint.

Categories of Fingerprints• A loop must have one or more

ridges entering and exiting from the same side. Loops must have one delta.

• Subcategories

– 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?

1. Loop (65%)

Categories of Fingerprints• Whorls have at least two deltas

and a core. • Subcategories

– Plain: at least one ridge makes a complete circuit

– Central pocket: no recurving ridge is touched in the pattern

– Double loop: made of two loops

– Accidental: a pattern not covered by other categories

2. Whorl (30%)

Categories of Fingerprints

2. Whorl (cont.)Distinguish between Plain and Central Pocket Loop• Draw in the pattern, which is a line between the

two deltas.

If the pattern line loops and touches the line twice - Plain

If the pattern line loops and does not touch the line - Central Pocket Loop

Categories of Fingerprints

3. Arch (5%) • Arches have 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 deltas or cores.

Subcategories

Plain

Tented

Ridge Characteristics

• Fingerprint analysis is done by careful study of ridge characteristics also called minutiae.

dot

ridge ending

eye

island

bifurcationbifurcation spur

trifurcation

bridge

ridge endingeye

bridge

bifurcation

island

bifurcation