Forensics Unit 4: Impressions Part 1

fingerprints

all fingers, toes, feet and palms are covered in ridges

fingerprint formation

basal layer collapses and folds to form intricate shapes

when prints form

near the 10th week of pregnancy

radial

u-shape, points toward radius (thumb) with 1 delta

ulnar

u-shape, points toward ulna (pinky) with 1 delta

plain arch

ridges go edge to edge with 0 deltas

tented arch

tent shape, pointy, with 1 delta (the tent)

plain whorl

2 delta’s holding up the whorl

central pocket loop whorl

whorl keeps going past the 2 delta’s

double loop whorl

s-shape, two loops crossing 2 delta’s

accidental whorl

jumbled, multiple delta’s

silver nitrate

technique used on wood or styrofoam, making a black/reddish colored print under UV light

superglue

technique used on plastic, metal, and glass, making a white colored print

ninhydrin

technique used on paper, making a purple/blue colored print

iodine

technique used on paper or cardboard, making a brown colored print

10 minutiae patterns

spur, bridge, delta, dot, double trifurcation, trifurcation, short ridge, eye, ending ridge

patent

2D visible prints/impressions transferred onto smooth surfaces by blood or other liquids

latent

2D prints/impressions made visible by dusting with powders or the use of chemicals

plastic

3D prints/indentations left in soft materials such as clay, wax, soap, or dust

information gathered from shoe prints

foot size, weight, height, job, personality, brand of shoe

steps of collection shoe impression evidence

1- take photos

2- take multiple photos

3- place a ruler

4- use oblique lighting when possible

luminol

substance sprayed on bloody footprints which makes them visible for photos to be taken

directly proportional

relationship between shoe size and height

tire tread pattern information

type of vehicle, link to a suspect on a scene, events revealed (class evidence)

tire track information

direction, model of car (individual evidence)

track width

from center of the driver’s tire to center of the passengers tire

wheelbase length

from center of front axle to center of rear axle (hood to trunk)

turning diameter

databases can be charged to find the vehicle with these specs

individual evidence

kind of evidence determined from an accident reconstruction

tire scrubs

determines the area of impact

skid marks

distance travelled after brakes are used

yaw marks

shows a sideways skid

dental impressions

individual evidence, shows characteristics of people’s teeth that can be unique

incisors

front teeth for biting food

canines

pointy teeth for tearing apart food

molar

back teeth for crushing food

dental age determination

baby vs. adult teeth

antemortem

before death, when swelling and bruising can distort the bite mark

postmortem

after death, when bruising and swelling don’t effect the visibility of the bite mark

dentin

a connective tissue that has calcified, gives the tooth its shape

enamel

calcium carbonate and calcium phosphate covering dentin

crown

above the gum line

root

embedded in the bony socket

neck

where crown and root meet

odontology

study of anatomy and growth of teeth

presumptive ID

personal effects, family ID, location of the body

positive ID

(based on certainty and is the gold standard) fingerprints, DNA, medical and dental records