Forensics; Exam3

Fingerprints

Used to identify people in civil and criminal cases

Fingerprint uniqueness

No two people have the same fingerprints (even twins)

Comparison evidence

Requires a known print to compare to an unknown

Ancient fingerprint use

Used in Qin Dynasty China for identification

Sir Francis Galton

Developed first fingerprint classification system

AFIS

Database used in the U.S. to store and analyze fingerprints

People v. Jennings (1911)

First case using fingerprint evidence in court

Friction ridge skin

Skin that forms fingerprints

Fingerprint development

Starts at week 12 and finishes by week 16 before birth

Fingerprint changes

Patterns stay the same but scars or wrinkles can be added

Ridges and valleys

Ridges are raised and valleys are grooves

Aging effects

Ridges flatten and skin becomes wrinkled

Injuries

Do not change pattern but add scars

Fingerprint types

Arch loop and whorl

Most common pattern

Loop (about 60%)

Delta

Triangular point where ridges split

Arch

Ridges enter one side and exit the other

Arch deltas

None

Types of arches

Plain arch and tented arch

Loop

Ridges enter and exit the same side

Loop deltas

One

Whorl

Circular pattern in center

Whorl deltas

At least two

Minutiae

Small ridge details that make fingerprints unique

Average minutiae

About 150 per fingerprint

Minutiae for identification

8 to 16 needed

Substrate

Surface where the print is found

Porous substrate

Absorbs moisture (paper wood)

Semi-porous substrate

Slightly absorbs moisture

Non-porous substrate

Does not absorb moisture (glass metal plastic)

Matrix

Substance that creates the print (sweat oil blood etc.)

Patent print

Visible print made with substances like blood or ink

Plastic print

Print left in soft material like wax or soap

Latent print

Invisible print made from sweat and oils

Visible prints processing

Photographed

Latent prints

Need enhancement to be seen

Fingerprint powders

Stick to oils to reveal prints

Black powder

Used on light surfaces

Grey powder

Used on dark surfaces

Fluorescent powder

Used on multicolored surfaces with UV light

Iodine fuming

Turns prints brown temporarily

Ninhydrin

Turns prints purple by reacting with amino acids

Amido black

Enhances blood prints

Superglue fuming

Hardens prints on non-porous surfaces

Lifting prints

Use tape then photograph

AFIS function

Stores and compares fingerprint data

AFIS input

High quality photo or scan

AFIS analysis

Compares patterns and minutiae