fingerprints

what is a fingerprint

an impression of the pattern of ridges on the last joint of a person’s finger

Dactyloscopy

study of fingerprints

Edward Richard Henry

in collaboration with Galton, instituted a numerical classification system

Fingerprints are ___ evidence

individual

What permits fingerprints to be classified

characteristic ridge patterns

Do fingerprints change during your life

no

How are fingerprints formed

formed during fetal development in the dermis, dermal papillae determine the ridge structure

What are the three basic fingerprint patterns

1. loop

2. whorl

3. arch

Loop requirements

one or more ridges which enter from one side of print and exit on the same side, one delta, one core

type of print and characteristics? (left hand)

here: loop, ulnar, one delta, one core

types of loops

• ulnar (points towards pinky finger, ulnar bone)

• radial (points towards thumb, radial bone)

whorl requirements

two deltas and a core, swirly shape

types of whorls

1. plain whorl (plain swirl, most basic)

2. central pocket whorl (whorl in a pocket, maybe enclosed in a loop)

3. double loop whorl (two loops next to each other that form the shape of a whorl)

4. accidental whorl (a combination of like everything to vaguely resemble a whorl)

type of print and characteristics

central pocket whorl, two deltas, one core

type of print and characteristics

plain whorl, two deltas, one core

type of print and characteristics

double loop whorl, two deltas, two cores

type of print and characteristics

accidental whorl

Arch requirements

ridges enter one side and exit opposite side

types of arches

• tented arch (sharp peak in the middle)

• plain arch (more subtle)

type of print and characteristics

tented arch

type of print and characteristics

plain arch

What are minutiae

specific points on a fingerprint where the ridge pattern changes

types of minutiae

• delta

• dot

• island

• spur

• bridge

• bifurcation (fork)

• double bifurcation

• trifurcation

• eye

• ridge ending

how many points of similarity are good to have between prints for forensics

8-12, but no legal requirements

Before computers, fingerprint analysts would…

manually compare evidence print to known prints which were classified into large books or card catalogs

IAFIS acronym meaning

Integrated Automated Fingerprint Identification System

IAFIS description

• made in the 70s

• computer searches files for prints similar to one given (taken from an individual)

• compare single print, usually latent print developed from crime scene

Finding a print at the scene

photographed before moved or disturbed

Three types of prints found at a scene

• plastic

  • 3d impression (wax, soap)

• visible

  • left by fingers coated with a colored substance (blood)

• latent

  • hidden or relatively invisible (need processing or developing to see)

What is a fingerprint made of?

Moisture, sodium chloride, amino acids, organic/inorganic, dead skin cells

Tools for developing prints

• flashlight

• powders

• magnifying glass

• brushes

• tape

• alternate light source

powder

• most common, adheres to moisture

  • regular or magnetic

• brushes —> camel hair, fiberglass, magnetic wand

• lifting —> use tape to remove powder, mount on a card

Developing latent prints

• Iodine

• Silver Nitrate

• Ninhydrin

• Superglue

Iodine

• highly toxic, done in a fume hood

• fabric, paper, untreated wood

• orangey-brown fingerprints

• fumes react with oils and fats

silver nitrate

• toxic, not used much

• reacts with salt in sweat

• paper, wood, fabric

• brownish-grayish print

Ninhydrin

• reacts with amino acids

• purple color

• non toxic, easy to use

• paper, fabric, wood

Superglue

• fumes react with water and sweat

• hard, whitish deposit

• fixes print to surface

• must be dusted and lifted (2 steps)