Fingerprint Principles

• According to criminal investigators, fingerprints follow 3 fundamental principles:

• A fingerprint is an individual characteristic; no two people have been found with the exact same fingerprint pattern.

• A fingerprint pattern will remain unchanged for the life of an individual; however, the print itself may change due to permanent scars and diseases.

• Fingerprints have general characteristic ridge patterns that allow them to be systematically identified.

Fingerprint Classes

• Fingerprints can be classified into three different groups based on the pattern of the ridges.

• Plain Arch (Tented Arch/Arches Ridges) enter on one side & exit on the other side.

• Loops (Radial Loop/Ulnar Loop) Ridges enter on one side & exit on the same side

• Whorls ( Double Loop Whorl/Accidental Whorl/Central Pocket/Whorl Plain) Consists of circles, more than one loop, or a mixture of pattern types

Dactyloscopy is the study of fingerprint identification. Police investigators are experts in collecting “dactylograms”, otherwise known as fingerprints.

Approximately 60% of people have loops, 35% have whorls, and 5% have arches.

Camel hair is the most common animal hair used to make fingerprint brushes. Now many brushes are made out of fiberglass.

The Automated Fingerprint Identification System (AFIS) is a computerized system capable of reading, classifying, matching, and storing fingerprints for criminal justice agencies. It uses computer algorithms to mark all minutiae points, cores, and deltas on the print, which are used to find possible matches with fingerprints in the database.

Ridge Characteristics

• Characteristics Fingerprints also have minutiae points, which are points where the ridge structure changes.

• These are useful in matching a fingerprint to a specific person.

Latent Prints

• Impressions left by friction ridge skin on a surface, such as a tool handle, glass, door, etc.

• Prints may be collected by revealing them with a dusting of black powder and then lifted with a piece of clear tape.

• Some investigators use fluorescent powder and UV lights to help them find latent prints on multi-colored or dark surfaces.

• Magnetic powder can also be used to reveal latent prints and works on shiny surfaces or plastic bags or containers.

• The cyanoacrylate fuming method (super glue method) is a procedure that is used to develop fingerprints on a variety of objects.

• Ninhydrin is a chemical that bonds with the amino acids in fingerprints and will produce a blue or purple color. It works well on paper or cardboard surfaces.

NCIC Codes

• Arches

  • Plain Arches: AA

  • Tented Arches: TT

• Loops

  • Ulnar Loop (toward pinky): Ridge Count 01-49

  • Radial Loop (toward thumb): Ridge Count + 50 50-99

  • radial loops on one hand would be ulnar loops on the other hand

  • a fingerprint impression is the mirror  image of the fingerprint on your finger

  • The loops are named after the bones in your forearm

• Whorls

  • The first letter in the code is the subtype.

  • The second letter is I, O, or M based on the tracing.

  • Plain Whorl: P_

  • Central Pocket Whorl: C_

  • Double Loop Whorl: D_

  • Accidental: X_

  • Can’t decide between plain and central pocket? Draw a line between the two deltas: If the line goes through the whorl, it is a PLAIN whorl.

  • To do a tracing, locate both deltas. Trace the ridge from the left delta past the right delta

    • Inner Tracing = I The tracing ends above the second delta

    • Outer Tracing = O The tracing ends below the second delta

    • Meets =M The tracing ends runs into or is within 3 ridges of the second delta

Henry Classification Code

• Prior to data bases, cards were filed based on their Henry Classification. Each finger is assigned a number ONLY if it has a whorl on it based on the chart.

• If someone has no whorls, their classification is 1/1. If someone has all whorls, their classification is 32/32.

• Now a 10 print card it used, along with the NCIC Code