By the end of this chapter you will be able to

Forensic Science: Fundamentals & Investigations, Chapter 15 1

Chapter 15 Cast and Impressions By the end of this chapter you will be able to:

distinguish between patent, latent, and plastic impressions

describe how to make foot, shoe, and tire impressions

use track width and wheel base information to identify vehicles

prepare dental impressions and match them with bite marks

All Rights Reserved South-Western / Cengage Learning © 2009


Introduction

People, vehicles, and objects leave evidence of their presence at an accident or crime scene.

Patent impressions are two-dimensional.

Latent impressions are hidden to the eye.

Plastic impressions are three-dimensional.



Shoe Impressions

The size of a shoeprint can tell the size of foot of the person.

The depth of a foot or shoe impression can tell something of the person’s weight.

The type of shoe can tell something of the person’s job or personality.

Databases contain the names of specific manufactures and tread patterns used to identify different types of shoes.


Shoe Wear Patterns

Some factors that personalize a person’s footwear include:

– Body weight.

– The way a person walks.

– The surface on which the person usually walks.

– Debris that became embedded in the tread or unique holes and

cuts in the tread.


Gait & Tracks

Numerous prints together tell an investigator about the person’s walking habits:

– Gait.

– Number of people.

– Movements of individual(s) at the scene.

– Entrance/Exit of scene.


Collection of Shoe Impression Evidence

Why would the following steps be important?

1. Take photos as soon as possible.

2. Take multiple photos of the impression from at least two different orientations.

3. Place an identifying label and a ruler in position with the impression for the photo.

4. Use oblique lighting when possible.


Lifting Latent Impressions

Different methods to make latent prints

visible include:

Luminol will make bloody footprints visible.

Dusting the latent print reveals an impression.

Electrostatic lifting and gel lifting (impression

shown above) techniques also can capture

hidden impressions.


Electrostatic Dusting and Lifting

Electrostatic dusting can reveal dust left with each step and create an impression.

Electrostatic charges can lift impressions from paper, carpeting, wood surfaces, linoleum, asphalt, and concrete.

Other methods to recover latent impressions include gel lifters.

These methods can provide information about the person who left the shoe print.


Tire Treads and Impressions

To channel water away and provide traction, a tire’s tread is divided into ridges and grooves.

Tires can leave patent, latent, or plastic tread patterns.

Tire evidence usually indicates the type of vehicle that left the mark, may be used to link a suspect or victim to a crime scene, and can reveal the events that took place.


Recording Tread Impressions

Ridges and grooves of discovered tire impressions are counted across the entire width.

Unique characteristics such as wear or pebbles embedded in the grooves are noted.

A print of a suspect’s tire impressions (through one revolution) is taken.

Comparison with impressions from the crime scene, then, can be made.


Identifying a Vehicle

Identifying tread patterns may not be enough to link a suspect with a crime scene. Other things can help with this:

– Front and rear track widths.

– Wheelbase measurement.

– Turning diameter.

Databases can be checked to find the vehicle with these specifications.



Accident Reconstruction

Drivers may not recall the exact series of events before, during, and after an accident.

People, vehicles, and objects, however, can leave evidence of their actions at the scene of an accident.

Debris patterns and tire marks, for example, can be clues to speed, direction, and vehicle identification.


Accident Reconstruction

There are three basic types of tire marks:

Skid marks—can be clues to the distance when brakes were applied and the vehicle’s speed.

Yaw marks—can show a sideways skid.

Tire scrub—can determine the area of impact.

How are each of these formed?


Dental Impressions

Occasionally a perpetrator will leave behind a bite mark.

Differences in the size of teeth and jaws, position, fillings, crowns, caps, breakage, and crowding make bite marks individual evidence.


Dental Patterns in Forensics

The investigation consists of recognizing, docu-menting, collecting, and analyzing evidence.

What are the two basic ways dental patterns can be used in forensic investigations?

Up to 76 points of comparison can be used when comparing a suspect’s dental patterns with bite marks left at a crime scene.

What is the common method used to reveal whether there is a match?


. . . . . . . . . . . . . . . . . Summary

Impression evidence—whether patent, latent, or plastic—will be considered class evidence unless it has individualizing features.

Debris patterns and tire marks can be clues to speed, direction, and vehicle identification.

Differences in dental patterns can connect a person to a crime scene.

Documentation (including photos early on) is extremely important in an investigation.

Documents

By the end of this chapter you will be able to