Fingerprinting

Bertino’s Forensic Science Ch. 6

Pre-notes

• Ink your prints on a practice piece of paper– Go easy on the ink.– Roll your finger prints approximately from nail

edge to nail edge.– The overall shape should be square.

• Finally (once you have the hang of it) on a clean piece of paper:– Ink all 10 of your fingerprints– Label the hand/finger

Characteristics

Core: center of the pattern

Delta: where the ridges go in different directions forming a triangle

Bifurcation: “fork in the road” where a ridge splits into 2 ridges

Ridges or friction ridges: raised area of skin on fingers & toes that assist in gripping objects/surfaces

Characteristics

Dot or island: a ridge ending that is as long as it is wide

Ridge ending: (ironically) where a ridge ends

Minutiae: all the characteristics & their position that makes a fingerprint unique

Type lines: diverging ridges surrounding a loop

Ridge Count

• Imagine a line from the delta to the core– Must cross at least 1 ridge– One ridge must be a looping ridge– Don’t count delta or core– Only count fragments or dots if they are as thick

as the surrounding ridges– If you cross a bifurcation, count both arms

What is the ridge count?

Class Characteristics

• Three primary types of fingerprints:

Loop Whorl Arch

What makes a loop a loop?

1. Ridge(s) that “boomerang”: 1 or more ridges entering from one side and “recurving” to exit the same side

2. Has a delta3. Has a ridge count across at least 1 looping

ridge

Types of loops

• Ulnar: opens towards pinkie finger or the ulna bone

• Radial: opens towards thumb or the radius bone

What makes a whorl a whorl?

• Type lines like loops and at least TWO deltas• Four types of whorls:– Plain whorl– Central pocket loop– Double loop whorl– Accidental whorl

Plain whorl

• At least one ridge makes a “circuit” around the pattern: may be any variant of a circle

• A line drawn between the deltas must touch/cross at least 1 of the “recurving” ridges of the inner pattern

Central Pocket Loop Whorl

• At least one ridge makes a “circuit” around the pattern: may be any variant of a circle

• A line drawn between the deltas must NOT touch/cross any of the “recurving” ridges of the inner pattern

Double Loop Whorl

• Two separate loop formations

• No “circuit” ridge• No imaginary line

between the deltas

What in the whorl? Accidental Whorl• A combination of 2

other patterns• Must have two or more

deltasOR

• A pattern that doesn’t meet the definition of any other pattern

What makes an arch an arch?

• Ridges flow in one side and out the other

• No deltas• Two types:– Plain (pictures)– Tented

Tented Arch

• Ridges at center form definite angle

• One or more ridges at the center forms an upthrust

• Approaching a loop: has only two of the three loop characteristics

Significance

• Loops: about 60% of the population– Radial loops are uncommon and if found are often located

on the index finger• Whorls: about 35% of the population– Central: about 2%– Double pocket: about 4%– Accidental: about 0.01%

• Arches: about 5% of the population– Plain: about 4%– Tented: about 1%

What causes fingerprints?

• Fetal development:– 6 weeks: hands/feets are like

paddles & volar pads begin to develop on hands/palms/feet

– 12/13 weeks: friction ridges start to develop in the epidermis & volar pads shrink to fit hands/palms/feet

– 18 weeks: ridges elevate– 21 weeks: print patterns are fully

formed

Friction Ridges

• Allows for better gripping– Found on hands, palms, feet

• Has no oil glands and no hair• Has lots of nerve endings• Makes up the “lines” or ridges of a fingerprint

Volar pads

• Tension & pressure of the volar pad (swollen tissue) affects the friction ridge pattern

• Placement of the volar pad appears to be genetic & is linked to specific pattern types– High centered volar pad: whorl type patterns– Low (can be result of fetal disturbance): arch or

low count loop– Intermediate: loop type patterns

Where are fingerprints?

• Epidermis: outside layer of skin; has ridges & pore openings

• Dermis: skin layer beneath epidermis

• Dermal papillae: boundary between dermis & epidermis; shapes epidermis

• Fingerprints originate in dermis