Forensic Science: Fundamentals & Investigations, Chapter 6 1

What Are Fingerprints?

o All fingers, toes, feet, and palms are covered in small ridges • Ridges help us grip objects

o Ridges are arranged in connected units called dermal, or friction, ridges• Complicated pattern of “hills” (ridges) and “valleys”

(furrows)o Fingers accumulate natural secretions and dirt o Fingers leave create prints on objects we

touch

Formation of Fingerprints

o Skin consists of: • Inner layer—dermis • Outer layer—epidermis• Basal layer in between

o Basal layer grows faster than the layers above and below it

o Basal layer collapses and folds to form intricate shapes

o Fingerprints begin forming near the 10th week of pregnancy

Forensic Science: Fundamentals & Investigations, Chapter 6 2

Forensic Science: Fundamentals & Investigations, Chapter 6 3

Characteristics of Fingerprints

o There are 3 general fingerprint distinctions:

ARCHAbout 5%

WHORLAbout 30%

LOOPAbout 65%

of the population

Forensic Science: Fundamentals & Investigations, Chapter 6 4

Characteristics of Fingerprints

o Forensic examiners look for• Core

(the center of a whorl or loop) • Deltas

(triangular regions near a loop) o Ridge count

• Counting from the core to the edge of the delta

• Distinguishes one fingerprint from another

Forensic Science: Fundamentals & Investigations, Chapter 6 5

Characteristics of Fingerprints

Forensic Science: Fundamentals & Investigations, Chapter 6 6

Characteristics of Fingerprints

Forensic Science: Fundamentals & Investigations, Chapter 6 7

Characteristics of Fingerprints

o Basic patterns can be further divided: • Arch patterns:

4% plain1% tented

• Whorl patterns: 2% central pocket4% double loop 0.01% accidental

o Even twins have unique fingerprints

Fingerprint Minutiae Patterns

o Formed by:• Ending abruptly

(ending ridge)• Splitting into two

ridges (bifurcation)• Being short (dot)• Can combine to form

additional patterns

Forensic Science: Fundamentals & Investigations, Chapter 6 8