1. Chapter 15 Cast and Impressions By the end of this chapter you will be able to:
Distinguish between patient, 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
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Forensic Science: Fundamentals & Investigations, Chapter 15

2. What is impression evidence?
Impression evidence can be defined as objects or materials that have retained the characteristics of other objects through direct contact.
Impressions are created when one object is pressed against another material with enough force to leave an impression of the object. 
Shoeprints, tool marks, tire tracks, bite marks, and marks on a fired bullet are several examples of impression evidence.
Impressions may be found in or on many different types of materials. The quality of the impression depends on the object making the impression and the surface conditions, such as how hard or soft it is and what type of material it is (soil, mud, dust, concrete, grass, skin, etc.)
CSI & Impressions
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3. Introduction Patient impressions are two-dimensional
People, vehicles, and objects leave evidence of their presence at an accident or crime scene.
Patient impressions are two-dimensional
Latent impressions are hidden to the eye
Plastic impressions are three-dimensional
Forensic Science: Fundamentals & Investigations, Chapter 15

4. Collection Methods
Investigators analyze the impression evidence to find unique characteristics to link shoes, tires, tools, and other objects found in a suspect’s possession to evidence at a crime scene.
Collection of impression evidence can be accomplished using several methods:
2-D: This type of impression is documented using photography. Some impressions may be dusted with fingerprint powder to be photographed or lifted with tape. They may also be collected using an electrostatic dust lifting process.
3-D: This type of impression can be documented using photography as well as by casting, which involves using dental stone or a similar substance to preserve the dimensional characteristics of the print.
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5. Shoe Print in Bio-Foam Impression Foam
Shoe Print Evidence
Investigators can analyze a shoe print to determine its class, or the type and brand of shoe. They will also look for individual characteristics, such as wear patterns and specific damages or defects.
Databases of shoe prints are available for investigators to help them determine the brand of shoe to provide leads for a case.
Depending on the quality of the impression, investigators may be able to determine a person’s speed (walking vs. running) as well as estimate the size of a person based on the impression’s depth.
Features to analyze:
Tread patterns, size, and depth
Wear patterns caused by the way a person walks
Material defects or damage (nicks, cuts, etc.)
Other trace materials, such as soil, tar, rocks, and paint that would indicate where a person has been
STAMP Database
Shoe Print in Bio-Foam Impression Foam
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6. 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
Databases contain the names of specific manufactures and tread designs
Forensic Science: Fundamentals & Investigations, Chapter 15

7. Shoe Wear Patterns Factors that personalize a person’s footwear:
Body weight
The way a person walks
Weight distribution
Direction of toes (straight, pointing out or in)
The surface on which the person walks
Unique holes, cuts, and debris embedded in the tread
Forensic Science: Fundamentals & Investigations, Chapter 15

8. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

9. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

10. 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
paper
carpeting
wood surfaces
linoleum
asphalt
concrete
Forensic Science: Fundamentals & Investigations, Chapter 15

11. Comparing Shoe Size and Height
Forensic Science: Fundamentals & Investigations, Chapter 15

12. Tire Track Evidence
Tire tracks are important in forensic investigations and are usually found in road accident scenes or in the access and escape routes of other crime scenes. Tracks help investigators identify the type of vehicle that left them. Investigators may make ink prints of a tire or plaster casts of a track. They will also take photographs that can later be used to prove a match.
Features to analyze:
Tread pattern
Width & depth of the tread pattern
Unique characteristics due to the wear pattern or defects
Tire databases are available help investigators determine the brand and model of the tire that left the impression , which can be used to determine the type of vehicle that made the tracks.
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13. Tire Treads and Impressions
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
Forensic Science: Fundamentals & Investigations, Chapter 15

14. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

15. Anatomy of a Tire
Forensic Science: Fundamentals & Investigations, Chapter 15

16. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

17. Identifying a Vehicle
Track widths— From center of tire to center of tire
Wheelbase length— From center of front axle to center of rear axle
Forensic Science: Fundamentals & Investigations, Chapter 15

18. Identifying a Vehicle Turning diameter
Databases can be checked to find the vehicle with these specifications
Forensic Science: Fundamentals & Investigations, Chapter 15

19. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

20. 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?
Forensic Science: Fundamentals & Investigations, Chapter 15

21. Bite Mark Evidence Video
Investigators can analyze bite marks for characteristics to help them identify victims or suspects as well as to exclude others. Marks can be left on a victim’s skin or other objects, such as Styrofoam cups, gum, or foods. Saliva or blood may be left behind that can be tested for DNA. Dental records including x-rays can also provide useful information, especially when attempting to identify a victim.
Features to analyze:
Type of bite mark (human or animal)
Characteristics of the teeth (position, evidence of dental work, wear patterns, etc.)
Color of area to estimate how long ago the bite occurred (old or recent bite)
Swab for body fluids for DNA tests
Bite Mark Evidence Video
Did you know?
The most famous incident where bite mark evidence led to a conviction, was in the case of the notorious serial killer, Ted Bundy. He was responsible for an undetermined number of murders between 1973 and 1978 and was finally tied to the murder of Lisa Levy through bites that he had inflicted on her body.
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22. 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
Forensic Science: Fundamentals & Investigations, Chapter 15

23. Development of Teeth
Forensic Science: Fundamentals & Investigations, Chapter 15

24. 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?
Forensic Science: Fundamentals & Investigations, Chapter 15

25. 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.
Forensic Science: Fundamentals & Investigations, Chapter 15