Fingerprints

History

• 3000 years ago… Chinese used fingerprints for legal papers

• 1880 Henry Fauld –first to use FP to ID criminals

• 1897 Sir Edward Richard Henry- -developed Henry classification

- based on all 10 prints- number/location of whorls

Skin

1. Epidermis- outer layer, no blood supply2. Dermis-internal layer- sweat glands that

produce water, salts, oils3. Papillae- at boundary of dermis and

epidermis

Prints- made of mostly water, salts, oil

Cross Section of Skin

AFIS

Automated Fingerprint Identification System

Matching points

Also known as:- Minutiae - Galton points

Based on types of ridges

Match ridges from a known print with an unknown print.

Types of Ridges

1. Ending ridge 2. Bifurcation (fork)3. Enclosure4. Short ridge5. Dot6. Eye (island)7. Bridge8. Double bifurcation9. Trifurcation

Fingerprints

• Friction ridges help human grip things

• Identical twins have different fingerprints.

• Fingerprints do not change over your lifetime.

• Scarring, etc can be used for ID

Deltas

• Delta- ridge that diverges

• Loops have one delta

• Whorls have 2 deltas

• Arches do not have deltas.

Types of Fingerprints

• 1. Arch

• 2. Whorls

• 3. Loops

Arches

Arches (no core or delta)• Plain• Tented

Whorls

• One or more ridges make complete circles• Two deltas and at least one core

Loops• Radial- loop opens to thumb• Ulnar - loop opens to pinky side

Pores

• Found randomly along the ridges

• Produce sweat

• Chemicals in sweat make the fingerprint that is left behind

• Pore location can be used to identify the person.

Process of IdentificationGet prints of all ten fingers from a person in question (suspect, victims, police, etc..)

Ways to get the 10 prints• Traditional ink and paper

• Roll colorless chemical on treated paper… chemicals react and the print becomes visible (newer)

• Live scan: roll prints on glass over video camera. Image is turned into digital information (newer)

Quality of prints

• Quality affected by:– Skill and experience of person taking the print– Cooperation of person giving the print– Damaged skin on people who work w/ their

hands– Rigor mortis– Decomposition, burned bodies

Types of Prints

• 1. Visible (patent)• Bloody prints

• 2. Plastic• Tacky paint• Putty• Clay• Soap

• 3. Latent• Invisible• Deposit sweat and oil

Methods to Develop Prints

1. Black powder

2. Magnetic powder

3. Iodine fuming (good on paper)

4. Silver nitrate

5. Ninhydrin ( for prints on paper)

6. Super glue (=cyanoacrylate)

7. Stickyside ™powder

Locating prints

• Shine flashlight at oblique angle• Gloves may leave impression• Less obvious places: under toilet seats,

toilet handles, tabletops, dresser drawers, surface of dinner plates, back of rearview mirrors, trunk lids of cars

• Use someone familiar w/ scene to tell if anything is different about the area

Equipment

1. Ultraviolet light (black light)Some substances will glow when exposed to UV

Ex. LSD– bluish-white

Ex. Certain fingerprinting powders glow under UV

2. Laser

3. Alternate light source– powerful light causes some materials to

fluoresce or luminesce

Daubert Hearings

• Fingerprint experts need to convince a judge that the methods used are valid.

• Daubert standards:– Has the expert’s scientific method been tested?– Has the expert’s method been the subject of peer

review and testing– What is the actual or potential rate of error?– do other scientists generally accept the expert’s

methods?

Odds and Ends

• If AFIS is used to locate a match, the final identification must be done by a human

• Palm prints can also be used• Latent prints can often be developed years later

as long as they don’t become wet• Fingerprints made from soot, insulation, face

powder are easily destroyed• Prints made from blood, ink, oil can last longer