Fingerprint Analysis

Have you ever wondered exactly what makes fingerprints unique? Here's what forensic professionals evaluate to determine the characteristics of a fingerprint.

Fingerprint Characteristics

Fingerprint Ridges

  • The dermal papillae are projected onto the surface of the epidermis as (fingerprint) ridges
  • The ridges are most pronounced on the fingers, palms, toes and soles of the feet (surfaces without hair)
  • The ridge patterns are individual characteristics
  • Function as friction ridges for extra gripping power
  • Formed in the fetus due to the amniotic fluid
  • Never change throughout life
  • Even identical twins have different ridge patterns

Characteristics of Fingerprints

  • The ridge patterns (minutiae) are characterized by type, number and relative location
  • An average fingerprint contains about 150 individual ridges
  • Individual ridges are sometimes called points

Examples of Ridge Patterns

  • ridge ending
  • short ridge
  • island
  • bifurcation
  • ridge crossing
  • enclosure

Matching of Fingerprints

  • Fingerprints are developed and lifted at the crime scene
  • Most lifted prints are partials
  • The fingerprint examiner makes a point by point comparison
  • Usually, 8 to 16 points must match to prove identity

Types of Ridge Patterns

  • Loops 65%
  • Whorls 30%
  • Arches 5%

Loops
Loops
  • One or more ridges enter from one side of a print, turn, recurve, and exit from the same side that they entered
  • Core: the approximate center of the loop pattern
  • Ulnar Loop: opens towards the little finger
  • Radial Loop: opens towards the thumb
  • Type Lines: the two ridges that diverge to surround the loop
  • Delta: the ridge point nearest the type line divergence
  • The number of ridges within the loop is an identifying characteristic

Plain Whorl

Central Pocket Loop Whorl

Accidental Whorl

Accidental Whorl
Whorls
  • Four types of Whorls: Plain Whorl, Central Pocket Loop Whorl, Double Loop and Whorl Accidental Whorl

Characteristics of All Whorls

  • Whorls have Type Lines
  • Whorls have at least two Deltas

Plain Whorls and Central Pocket Loops

  • Have at least one ridge (the spiral ridge) that makes a 360o circuit as a circle, oval, or spiral
  • Plain Whorl: a line drawn between the two deltas crosses a spiral ridge
  • Central Pocket Loop: a line drawn between the two deltas does not cross a spiral ridge

Double Loop Whorls and Accidental Whorls

  • Double Loop Whorl: Two loops combined in the same pattern, usually opening in opposite directions
  • Accidental Whorl: two or more patterns in the same print. For example, a loop + a plain whorl, or a loop + an arch, etc

Plain Arch

Tented Arch
Arches
  • Arches do not have type lines, deltas, or cores
  • Plain Arch: Ridges enter from one side of the pattern and exit out the other side
  • Tented Arch: the center of the pattern contains a sharp upthrust. A tented arch may resemble a loop, but lacks one of the characteristics of a loop

Automated Fingerprint Identification System (AFIS)

  • Computer scanners identify ridge endings and bifurcations, and their relative positions are mapped
  • Prints lifted at the crime scene are compared to fingerprint file cards
  • A group of suspect fingerprint cards is identified
  • The examiner must then do a point by point comparison
  • The computer can compare the suspect's print to 500,000 fingerprint cards in less than a second
  • This speed makes it possible to compare a single print from a crime scene to the entire fingerprint card file!
  • Computer enhancement can compensate for imperfections in lifted latent prints