Fingerprints

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What Are Fingerprints? •Impressions (of ridges) made by fingers, toes, feet, and palms

• Ridges help us grip objects

• Ridges are arranged in connected units called dermal, or friction, ridges

• Fingers accumulate natural secretions and dirt

• Fingers leave create prints on objects we touch

FingerprintsA fingerprint pattern will remain unchanged for thelife of an individual; however, the print itself maychange due to permanent scars and skin diseases.

Characteristics of Fingerprints

o Forensic examiners look for

• Core(the center of a whorl or loop)

• Deltas (triangular regions near a loop)

• Ridge count

• Counting from the core to the edge of the delta

• Distinguishes one fingerprint from another

Even though every person has a unique fingerprint, we can categorize fingerprints into 3 groups.

There are 3 general fingerprint distinctions:

Fingerprint ClassesThere are 3 specific classes for all fingerprints based

upon their visual pattern: arches, loops, and whorls.

Each group is divided into smaller groups

as seen in the lists below.

Arch

Plain arch

Tented arch

Loop

Radial Loop

Ulnar loop

Whorl

Plain whorl

Central pocket whorl

Double loop whorl

Accidentical

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

Basic patterns can be further divided: • Arch patterns:

• 4% plain• 1% tented

• Whorl patterns: • 2% central pocket

• 4% double loop • 0.01% accidental

Even twins have unique fingerprints

Fingerprints

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Why are fingerprints useful?Properties that make a fingerprint useful for ID:• It’s unique characteristic

ridges.• It’s consistency over a

person’s lifetime.• The systematic classification

used for fingertips.

(The FBI uses a 10-print card for fingerprints)

Ridgeology: The study of the uniqueness of friction ridge structures

and their use for personal identification.1

As we have learned in our first lesson, a

fingerprint is made of a series of ridges and

valleys on the surface of the finger. The

uniqueness of a fingerprint can be determined by

the pattern of ridges and valleys as well as the

minutiae points, which are points where the ridge

structure changes.

Fingerprint Identification

When minutiae on two different prints match, these are called

points of similarity or points of identification. At this point there

is no international standard for the number of points of

identification required for a match between two fingerprints.

However, the United Kingdom requires a minimum sixteen points

while Australia requires twelve.

Automated Fingerprint Identification System (AFIS)

AFIS is a computerized system capable of reading,

classifying, matching, and storing fingerprints for

criminal justice agencies. Quality latent fingerprints

are entered into the AFIS for a search for possible

matches against the state maintained databases for

fingerprint records to help establish the identity of

unknown deceased persons or suspects in a criminal

case.

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Use these characteristics as points of identification when comparing fingerprint

samples. The more points you can find in common, the better the match!

http://cnx.org/content/m12574/latest/properties.jpg

Ridge Characteristics

Crossover

Core

Bifurcation (fork)

Ridge ending

Island

Delta

Pore

Scar

http://www.dkfz.de/tbi/projects/bmcv/images/iu_it246_04s_fingerprint1.jpg

How many ridge characteristics can you identify in this fingerprint?

IAFIS The FBI's Integrated Automated Fingerprint Identification System (IAFIS) is the largest biometric database of criminals in the world. Clear, legible fingerprints form the foundation of the Fingerprint Master File, which continues to grow by approximately 13,000 records each day.

Fingerprints

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How to take fingerprints

Type 4 – Rolled impressions are the ten individually taken fingerprint images rolled from nail to nail. The plain impressions are used to verify the sequence and accuracy of the rolled impressions.

Type 14 - Identification flat impressions are taken simultaneously without rolling. These are referred to as plain, slap, or flat impressions. The individual's right and left four fingers should be captured first, followed by the two thumbs (4-4-2 method). Instituting this finger capture method ensures the highest level of fingerprint sequence accuracy.

IAFIS – Rolling Prints Facts

Recommended height for recording legible fingerprints is approximately 39 inches from the floor.

This allows the forearm of an average adult to be parallel with the floor. This is the recommended position to record fingerprints

If using the ink and paper method, roll the finger on the inking plate or pad so the entire fingerprint pattern area is evenly covered with ink.

Ink should cover from one edge of the nail to the other and from the crease of the first joint to the tip of the finger. Using the correct amount of ink is vital

IAFIS – Rolling Prints Facts

The side of the finger bulb is placed upon the card or platen.

The finger is then rolled to the other side until it faces the opposite direction.

Care should be exercised so the bulb of each finger, from tip to below the first joint, is rolled evenly.

When using the ink and paper method and a rolled impression is not acceptable, you may use an adhesive retab to cover the fingerprint in its space. (Only two retabs can be applied to each fingerprint block.)

Types of Fingerprints

There are 3 types of prints that investigators look for at crime scenes:

1. Patent fingerprints—visible prints transferred onto smooth surfaces by blood or other liquids

2. Plastic fingerprints—indentations left in soft materials such as clay or wax

3. Latent fingerprints—made visible by dusting with powders or the use of chemicals

Fingerprint Forensic FAQs • How are latent fingerprints collected?

Visualizing Latent Prints

Also called developing latent prints.

Methods:• Dusting: carefully dusting it with a fine powder

---best on hard, nonabsorbent surfaces.--color of powder chose to stand out against surface.--developed print lifted by means of clear sticky tape.

• Iodine (chemical): reacts with fatty oils from the finger to form a visible but short lasting print.

--works best for prints on porous paper.

Visualizing Latent Prints

Chemical Methods of Developing (Continued):• Ninhydrin: reacts with amino acids left by the finger to make an

orange to purple image--best with paper and porous surfaces

• Silver Nitrate (AgNO3): reacts with salt (NaCl) left from perspiration in a dried print to form silver chloride (AgCl), which is then converted to dark silver oxide (Ag2O).

• Superglue: evaporating superglue in an enclosed container. The glue (cyanoacrylate ester) reacts with print residues to make a white permanent impression that can be treated with powders or fluorescent dyes to make a sharper contrast for photography or lifting.