1. Impression Evidence
“What does it tell us?”

2. How can an impression be used to solve a crime?
Essential Question:
How can an impression be used to solve a crime?

3. Impressions
An object or surface takes the form of another through direct contact.
Two types:
2 dimensional: transfer of an imprint to a firm substrate (glass, paper, floors, etc.)
EX: lip print on a glass window
3 dimensional: transfer of an imprint to a soft substrate (mud, grass, snow, etc.; usually outdoors)
EX: footprint in mud
Substrate: the surface/object/organism/enzyme being effected
2D examples: usually found indoors on surfaces like counter tops, glass, paper, cardboard, ceramic floors and waxed floors
-fingerprint
-black tire tread mark on a paved road
3D examples: usually found outdoors in mud, sand, grass, dirt, clay, tar, or snow
-tire mark in the dirt
-a bite mark on your arm

4. Reasons for examining impressions: it is evidence!
May prove that a crime has been committed
Establish key elements of a crime
Link a suspect with a crime scene or a victim
Establish the identity of a victim or suspect
Corroborate verbal witness testimony
Exonerate the innocent
Give detectives leads to work within the case

5. Ways to Recover Impressions:
Mechanical processing:
Brush and Powder method
Tape lift
Used for 2D impressions
Ex: footprints on a waxed floor
Casting:
Making a replica of the impression
Filling a 3D form with a material mold that will not destroy the impression
Used for 3D impressions
Ex: Tool marks on a window sill or tire impression in the mud
Electrostatic Lifting:
A charge is used to lift dry materials from the surface to a black film
Ex: Shoe impression on a dusty floor
Oblique angle photography:
method of documenting impressions
Impressions in dust are obviously extremely delicate, though can be carefully recovered using electrostatic treatment. An electrostatic lifter passes a voltage across a thin layer of conductive film, which is composed of a lower layer of black insulating plastic with an upper layer of aluminium foil. The electrostatic charges cause particles of the impressions to jump onto the black underside, recovering the dust impression

6. Ways to Enhance Impressions:
Dyes:
Used on glass or marble surfaces
Luminol:
Chemical with luminescent properties activated upon contact with the iron in blood
Ex: may be applied to enhance a bloody footprint
Alternative light:
Used on porous surfaces like wood or paper
Ex: Black light
Dusting:
Powder and brush

7. Think: Individually answer this question:
Which technique for collecting impressions would be best for lifting bite marks from a victim? Explain.
You have 2 mins!

8. Do you both agree on the same technique?
Pair & Share:
Discuss your answer with a partner
Do you both agree on the same technique?
You have 2 mins!

9. Types of Impressions: Foot impressions Bite marks Tire impressions
Tool marks

10. Bite Marks Can be as complex as a fingerprint
Individual evidence
Dental records & X-rays are often used to identify individuals
Show position of teeth, fillings, etc.
What they may tell you:
Can identify a suspect or victim
Most often indicate assault or sexual attack
Are common with domestic violence
Dental xrays: show position of teeth, fillings, wear…

11. Bite Marks 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
Teeth are one of the hardest substances in the human body, so they are frequently well preserved.
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.

12. Bite Marks Age determination Milk teeth present: generally under 12
Wisdom teeth present: yrs old

13. Shoe Impressions The most commonly missed evidence at a crime scene
Class characteristics:
Size
Manufacturer
Model
Type
Individual characteristics:
Gait-manner of moving the foot
Wear of shoes, esp. outsoles
Outsoles: outer soles of shoes at bottom
Damage
cuts, gouges, chunks…
debris
nails/screws
Shoeprint databases used
ex: SloMate and TreadMark
Length of stride and the way the footprint digs in the ground can suggest running
wear - the gradual erosion of rubber due to frictional forces

14. Shoe Impressions What they tell you: Number of suspects
Corroborate or dispute alibis and witness testimony
Can link two crimes
Link a suspect to a victim or crime scene
Point of entry/exit
Position of the suspect, victim, and/or witness
Pathway through the crime scene
Direction of travel
Time period (from temporary impressions such as in snow or dew)
Also tell you the sequence and manner (walking, running, limping, staggering) in which the impressions were created.

15. Shoe Impressions What they tell you continued:
Size: approximate height of an individual
Put heel to wall and measure left foot from wall to tip of the big toe.
The length of an adult’s foot is about 15% of his/her height
This percentage varies in growing individuals

16. Shoe Impressions 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

17. Ticket to leave
On a sheet of paper, WRITE THE QUESTION & ANSWER to these true or false questions:
1. T or F. Impressions are the most apparent pieces of evidence at a crime scene
2. T or F. There are two types of impressions:2D and 3D impressions.
3. T or F. Casting can be used to lift a shoe impression in the dirt
4. T or F. Approximate age is determined through bite marks.
5. T or F. Bite marks are individual evidence.

18. Tire Impressions What they tell you: Type of tire
Make or model of the tire
Direction of travel after and/or before the crime
Number of vehicles present
May eliminate a suspected tire
Match a tire to a suspect

19. Tire Impressions Features to analyze: Wheelbase Stance = Track width
Distance between the center of the front tire and the center of the back tire.
Stance = Track width
Distance between the two front tires or the two back tires
Class characteristics
Ex: size, tread design
Individual characteristics
Ex: Cuts, gouges, wear,
debris (rocks, nails)
individual characteristics can be used to identify an exact tire.
individual characteristics change over time
Cuts, Gouges, Chunks, Etc.
Specific Wear Details
Rock or Other Debris Holds
Nails/Screws
Class Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track.
Size
Tread Design
Noise Treatment
Mold Variations
Overall Wear

20. Tool Marks Types of Tool Marks:
Compression: substrate caught between two opposing forces (pinching or shearing marks)
Wrench, pliers
Sliding: a tool scrapes across a substrate causing parallel striations
Screwdriver

21. Tool Marks What they tell you: Type of tool used
Size and shape of the tool used (class characteristics)
Rule out suspected tools
Shape and pattern of imperfections (individual characteristics)
Can be matched to tools in suspect’s possession
Entry/exit to crime scene

22. Tool Marks How are tool mark impressions collected?
Pictures of tool mark
Casting using plaster or silicone
Collecting by casting
Never put comparison tools in original toolmark

23. Admissibility of Evidence
Probative value
3 standards:
Relevance
Proves or disproves a fact of the crime
Competence
Reliability of the evidence
Materiality of evidence
Proves an essential fact of the case
Relevance ex: A tool stained with a suspect's blood might be relevant, for example, but so is the person who sold that tool to the suspect. However, testimony from a toddler discussing a broken house contract would be deemed irrelevant and therefore inadmissible because a child would be too young to understand the case.
Competence ex: matching fingerprints, the results of a DNA test, or an expert on footwear impressions
Material ex: if a lawyer attempts to prove that the drapes in the room of a murder scene were blue, chances are a judge will deem such evidence immaterial. The room itself may be relevant to the case, but it's likely the color of the drapes doesn't have anything to do with the murder.

24. Georgia Performance Standard
SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science.
d. Evaluate the relevance of possible evidence at the site of an investigation.
SFS4 Students will evaluate the role of ballistics, tool marks and evidence of arson in forensic investigation.
c. Recognize the forensic significance of tool marks, footwear and tire impressions in an investigation.