Footwear/Tire Impressions Notes

The pattern produced by impressions are what orientation?

Mirror-image

2D Impressions (Imprints)

Have length and width, but no depth

Typically on a hard surface

3D Impressions (Indentations)

Have length, width, and depth

Typically on softer surfaces

Dry Origin Impressions

Shoe and substrate are dry when impression is made

Dust is generally material transferred

Wet Origin Impressions

Shoe and/or impression is wet when impression is made

Positive Impressions

Residue visually represents the areas that were in contact

Negative Impressions

Contact areas remove residue from surface

Documentation of Pattern Evidence

Photograph first, and then attempt to recover

Recovery Methods

Cast (3D impressions)
Lift (2D impressions)

Quality Photographs must include:

Scale, label, use a tripod, film plane parallel to the impression, detached flash at several angles, several exposures

F.U.S.S Acronym

Fill the frame, Use a scale, Sidelighting, Several SHots

Oblique Lighting

Should be used in addition to natural lighting

Provides greater amount of contrast and detail

Dust prints should be visualized with:

Oblique lighting

When an impression is lifted or casted, the orientation is:

The same as the original orientation

Electrostatic Lifting

Device applies electrical charge to lifting film placed over a dust print. Film is drawn to the surface by static electricity. Dust particles in impression attract to lifting film

Electrostatic Lifting is:

Non-destructive, often need oblique lighting to visualize

Collection of lifts:

Taped to manila folders or boxes, or carefully rolled up and placed in a tube

Gelatin lifter

High quality elastic sheets of rubber with a low adhesive gelatin layer on one side

Chemical Enhancement methods for bloody impressions

LCV Spray - Dark violet color

Amido Black - Dark blue-black color

Snow Print Wax

Can be sprayed into an impression to help protect it while casting

Shoeprint Databases

SICAR and FPX

Sizing

Sizing should try to be determined. Must be given in a range

Why must we give a range for sizing?

Error, movement altering image, same size outsole on several shoes, specific dimensions vary, knock-off brands

Useful Information from Tire Tracks

Crime scene reconstruction, possible vehicle make and model, an approximation of mileage on tire, comparison to know tires

Tread Pattern

Includes multiple ribs, blocks, lugs, or a combination of all three

Rib

A continuous strip of tread rubber around a tire’s circumference. Multiple side-by-side ribs are usually molded across a tire’s tread.

Block

Also known as an “element.” Freestanding, independent tread blocks that are positioned around the tires circumference

Lug

Extra large, freestanding, independent lugs positioned around the tire’s circumference.

Circumferential Grooves

Major grooves molded around the tire

Lateral grooves

Major grooves molded across the tire

Tie Bars

Short rubber links molded across lateral grooves between adjacent tread blocks

Sipes

Typically featured in all-weather/season tires, thin slits molded into an otherwise smooth tread surface

Noise treatment

The varied arrangement of different pitch lengths of tread elements around the circumference of the tire

Tread wear indicators

Raised areas in specific locations to determine when a tire should be replaced

Tread wear

Progressive wearing-away of a tire due to abrasion. General wear pattern is predictable for tires

How long should a tire test impression be?

6-8 feet for a full rotation

Tire Test Impression Methods

Sectioned by tread wear indicator and can use magna-brush, lacquer spray, vegetable oil/shoe spray