Impression Evidence

Patent

visible impression that is 2D

Latent

Hidden impression that is visualized by a chemical or physical development

Plastic

3D impression

What characteristic of footwear are class characteristics and why?

size, tread, pattern, and brand because they are not unique.

Describe what can be determined from shoe impressions at a crime scene and after analysis at a crime lab.

- size of footwear

- brand of footwear

- sex of wearer

- weight of wearer

- type of footwear

How must shoe impression evidence be collected and preserved at a crime scene?

• photo that includes a ruler

• lifting with electrostatic dusting or gel lifting

• casting with plaster of Paris (CaSO4) or dental stone (on snow)

How are latent shoe impressions collected from a crime scene?

1. mylar film covers print

2. apply voltage with electrode and electrostatic unit

3. use roller to roll over print

4. lift dust prints

Describe why shoe wear patterns are important in analyzing shoe impressions from crime scenes.

Can tell:

• walking habits

• shape of feet

• body weight

• activities engaged in

• surfaces walked on

• unique debris, holes, or cuts

Describe how casts are made of impressions at a crime scene in snow.

• snow impression wax sprayed at 1-2 min interval 3 times (light coat)

• Wax allowed to dry for 10 minutes

• pour viscous mix of dental stone.

• Dries

Describe how casts are made of impressions at a crime scene in sediment.

• spray the impression with an adhesive

• pour plaster inside the impression.

• Dries

How are impression databases used for analysis of evidence?

Have information that can tell you what or who the impression belonged to. Can also tell you if the imprint was seen at another crime scene.

How are human teeth impressions analyzed from crime scenes?

• position

• size of teeth and jaw

• evidence of dental work

• wear pattern

What characteristics of tires would be analyzed at a crime scene

• ridges and grooves

• tread

• wheel base measurements

• print of tire through one revolution

What is a tool mark?

Any IMPRESSION, CUT, GOUGE, or ABRASION caused by a tool coming in contact with another tool.

What types of tools produce indentations?

tools pressed against a softer surface to create a negative impression

ex. screwdriver or crowbar

What types of tools produce abrasions?

When surfaces slide across one another. Grip and Turns

ex. wrench

What type of tools produce cutting marks

Produced along edge of surface that is cut.

ex. knife, saw, wire cutters

How can class and individual characteristics be determined from tool marks?

Class: size and shape of tool

Individual: minute imperfections on a tool