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

Introduction Impressions fall into three basic categories: People, vehicles, and objects leave evidence of their presence at an accident or crime scene. Impressions fall into three basic categories: 1. Patent impressions are two-dimensional, ex. Blood print 2. Latent impressions are hidden to the eye 3. Plastic impressions are three-dimensional, ex. Mud, snow, soil *Depending on how it is made, impression evidence may be either class evidence (type of shoe) or individual evidence (wear pattern)

Shoe Impressions Shoeprint size indicates the foot size The depth of a foot or shoe impression indicates a person’s weight The type of shoe can tell something of the person’s job or personality When a shoe impression is found at a crime scene, the crime scene investigator will search Databases contain the names of specific manufactures and tread designs

Shoe Wear Patterns Factors that personalize a person’s footwear: Walks on toes or heels Body weight Walks straight ahead or toes inward or outward Shape of the foot Surface on which the person usually walks Unique holes, cuts or debris

Gait and Track Numerous prints together tell an investigator about the person’s gait, or walking habits. Information that can be obtained from shoe impressions include; The number of people Movements (one room or several) Entrance or exits.

Collection of Shoe Impression Evidence Why would the following steps be important? Take photos as soon as possible Take multiple photos of the impression from at least two different orientations Place an identifying label and a ruler in position with the impression for the photo Use oblique lighting when possible

Lifting Latent Impressions Different methods to make latent prints visible: Luminol makes bloody footprints visible for photography Dusting the latent print reveals an impression for lifting or photography Electrostatic lifting and gel lifting (image below) techniques can capture hidden impressions

Electrostatic Dusting and Lifting Electrostatic dusting reveals dust left with each step and creates an impression Electrostatic charges can lift impressions from Gel lifters also recover latent impressions by dusting and then placing the gel between paper backing and a plastic cover sheet paper carpeting wood surfaces linoleum asphalt concrete

Casting Three dimensional impression, such as a shoeprint in mud or snow, is called a cast and may be made to preserve physical evidence. The casting material used for snow is called dental stone, it hardens faster than Plaster of Paris.

Comparing Shoe Size and Height

Tire Treads and Impressions Motor vehicles can leave patent, latent, or plastic patterns Tire treads—ridges and grooves channel water away and provide traction Patent tread patterns—impressions made after tire runs through a fluid material Latent tread patterns—impressions from tire oils used to keep tires soft and pliable Plastic tread patterns—three dimensional impressions left in soft surfaces

Tire Treads and Impressions Tread patterns can indicate the type of vehicle that left the mark Link a suspect or victim to a crime scene Reveal events that took place at the scene

Anatomy of a Tire A tire’s tread surface is divided into ridges (elevated regions) and grooves (indentations)

Recording Tread Impressions Count ridges and grooves across the tire width Note unique characteristics—wear or pebbles embedded in the grooves Create a print of the suspect’s tire impressions through one revolution Compare impressions from the crime scene and suspect’s tire Identifying tread patterns may not be enough to link a suspect with a crime scene

Identifying a Vehicle Track widths— From center of tire to center of opposite tire Wheelbase length— From center of front axle to center of rear axle Wheelbase Track width

Identifying a Vehicle Turning diameter A measure of how tight a circle can be driven by a vehicle OR the minimal space required for a car to make a U-turn. Databases can be checked to find the vehicle with these specifications When a vehicle turns a sharp corner, even at moderate speed, a track is created by the additional stress put on the front out tire.

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 can be clues to speed, direction, and vehicle identification

Accident Reconstruction There are three basic types of tire marks: Skid marks—clues to the distance traveled after brakes are applied and the vehicle’s speed Yaw marks—shows a sideways skid Tire scrub—determines the area of impact How are each of these formed? Through experience and experimentation, investigators can also estimate speeds of vehicles using the “skid-to-stop” formula. (weight of car, texture of surface and length of skid marks determines speed)

Dental Impressions Occasionally a perpetrator will leave behind a bite mark—considered individual evidence Note differences in the size of teeth and jaws, position, fillings, crowns, caps, breakage, and crowding

Tooth Anatomy Protects the living dentin, hardest substance in the human body - Calcium and Phosphate, similar to bone 27 baby teeth 32 permanent adult teeth including wisdom teeth (usually 17 years old) 8 incisors (front) 4 upper, 4 lower 4 canines (beside the incisors) 2 upper, 2 lower 8 premolars 4 upper, 4 lower 12 molars 6 upper, 6 lower

Development of Teeth The approximate age of a child can be estimated by viewing the child’s teeth. Older child may have a mixture!

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? There are 76 points of comparison 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? Identify remains Identify suspect photograph

. . . . . . . . . . . . . . . . . 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 early photos) is extremely important in an investigation.