casts and impressions

impressions

impression evidence

considered to be class evidence unless there are unique and distinguishing characteristics that make it individual.

what type of evidence is dental work

individual evidence

dental impressions

only circumstantial evidence

patent impressions

Visible (object picks up soil, dist, paint, blood, or other material and transfers it)

plastic impressions

left in soft materials (snow, mud, soil, or blood)

latent impressions

Hidden from the unaided eye; Made visible through dusting, electrostatic techniques or with chemicals

shoe and foot impressions answer questions

What were the entrance and exit routes?

How many people were at the crime scene?

Were the people moving? If so, what direction?

tread pattern

Shoe size, type of shoe

wear patterns

factors that personalize footwear, shape of foot, body weight, pressure on outside of heel rather than inside, unique holes, cuts and debris

gait

a pattern of moving

stride

the length of one step

photographing

Take photos in situ (as it appears)

Lens perpendicular to the impression to reduce distortion

Indirect/oblique

lifting impressions

luminol or blue star, powders

casting

dental stone, plaster of paris

two dimensional prints

Dirt or other material picked up by the shoe and deposited onto a flat, hard surface, impressions left behind in dust, wax, polish

three dimensional prints

made in soft materials like dirt or snow

ribs

ridges running around the circumference of the tire

grooves

indentations

track width

measured from the center of the tread of a tire to the center of the tread on the opposite tire

wheelbase

distance between the center of the front wheel and the center of the rear wheel

how long should tire impression collections be

at least 3 meters long to ensure the tires make a complete rotation

skid marks

accelerating or decelerating quickly, Dark to light or light to dark, Leaves straight tire marks

yaw marks

tire rolls but simultaneously; always curved, stripes form on pavement as tire is dragged laterally

tire scrubs

used to determine area of impact

When bite marks are found on the skin (which is somewhat elastic) or stretchable clothing

the accuracy of measurements is always in question

for dental evidence to be admissible in court

at least two forensic dental experts must agree on the identification