Concept Animation: Fingerprinting

Introduction

Figure 1: A fingerprint

The patterns of raised skin found on the fingers of every individual are known as fingerprints (Figure 1). Fingerprints develop in the womb, and except for changing in size during growth, the pattern of each fingerprint will remain the same throughout a person's life. They are biometrics, measurable biological features used for identification purposes. Forensic investigators utilize fingerprints to corroborate evidence that a suspect was present at a crime scene. If fingerprints are properly collected and in good condition to be analyzed, they may be admissible in court.

Skin and Fingerprints

Figure 2: Basic skin anatomy

The skin consists of three layers of tissue: the epidermis, dermis, and hypodermis (Figure 2). The epidermis is the outermost layer of skin, and certain areas have a feature called friction ridge skin. The palms of the hands, fingers, soles of the feet, and toes have raised lines called ridges and grooves. Depressed areas between the ridges are called furrows. Friction ridge skin, along with pores (the tiny openings in the skin that secrete sweat and oils), allow the hands and feet to firmly grasp surfaces. Friction ridge skin forms in the 12th to 16th week of fetal development through a combination of genetic and environmental factors. Therefore, a person's genetic make-up is coded to dictate how friction ridge skin will form, but random events, such as fetus's position at a particular moment or the composition and density of surrounding amniotic fluid, influences how every individual's fingerprints form into a distinctive pattern.

Figerprint Characteristics

Print ridges on finger tips are found in basic patterns with small, distinguishable variations known as minutiae (Table 1). The three basic patterns of finger friction ridge skin include:

Table 1: Common Ridge Minutiae
Name	Illustration
Bifurcation (Fork)
Double Bifurcation
Dot
Delta
Ridge Ending
Eye
Bridge
Island
Spur
Trifurcation

Figure 3: Loop ridge pattern. The area shaded red highlights the looped shape.

Figure 4: Plain whorl ridge pattern.

Figure 5: Plain arch ridge pattern.

• Loop: Ridges enter from one side of the finger (either left or right), form a loop or hairpin turn, and exit from the same side of the finger tip from which they entered. Loop patterns can be further classified as radial loops (enter and exit toward the thumb) or ulnar loops (enter and exit toward little finger). More than 50% of people have looped fingerprints, making it the most common pattern (Figure 3).
• Whorl: Ridges form almost concentric circles or spirals in the center of the finger tip. Whorls can be further classified as plain whorls, central pocket loops (one ridge that makes a complete circuit without touching another ridge), double loops (two loops within the whorl), and accidental whorls (combination of other patterns). About 30% of people have whorl ridge patterns (Figure 4).
• Arch: Ridges enter from one side of the finger tip, create a wave or tent shape, and exit on the opposite side from which they entered. Arch patterns can be further classified as plain arches or tented arches (sharper rise than plain arch). This is the least common fingerprint pattern (Figure 5).

Fingerprint Analysi

Not all fingerprints collected at a crime scene can be used to find a match to a suspect. Partial fingerprints or fingerprints collected from certain surfaces that result in a poor quality print may not reveal enough ridge detail to distinguish minutiae. In addition to the quality of a collected fingerprint, there are other factors that need to be considered when analyzing a fingerprint. While it is accepted that fingerprints are unique to every person, no scientific studies have confirmed the uniqueness of a fingerprint or defined a standard for what constitutes a match. For some prints, eight points may be sufficient. Others may require more to support a conclusion. Examiner skill, experience, subjectivity, and bias may also affect the determination of a fingerprint match. There have been cases in which multiple experienced fingerprint analysts have declared a match between a fingerprint and a suspect who was later proven to be not guilty.

Computer programs, such as the Integrated Automated Fingerprint Identification System (IAFIS) used by the FBI and state and local authorities, are used to standardize fingerprint analysis and aid in narrowing possible matches from millions of fingerprints in a relatively short amount of time.

Experiment Demonstration: Before you begin, feel free to review the following demonstration of an experiment in this lab.

Lab Drill: Fingerprinting