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.

SubcategoriesPlainTented

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