1. Impressions
CHS
Forensics

2. Types of impressions
Tool Marks
Shoe Prints
Tire Tracks
Bite Marks

3. Tool Marks
A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.
Most often tool marks are encountered at a burglary scene that involves forcible entry.

4. Tool Marks cont.
Typically tool mark impressions are left behind on the frame of a door or window.
Careful examination of the marks can yield class characteristics, size and shape of the tool.

5. Tool Marks cont.
Small random striations during manufacturing of the edge of a pry bar, chisel, screwdriver, or knife will have microscopic irregularities, ridges and valleys.
These irregularities are enhanced by usage, where the tool, through use, can become damaged giving individual characteristics.

6. Tool Marks cont.
When the tool is scraped against a softer material these minute marks are left behind.
These minute marks are matched to the suspected tool using a comparision microscope.

7. Tool Marks cont.
When the evidentiary materials cannot be brought back to the lab or is to big to be placed under the microscope, casts are made of the tool marks using liquid silicone .

8. Tool Marks cont.
Under no circumstances is the suspected tool and the evidentiary material to come into contact.
This could compromise the evidence and will cast doubt on the integrity of the evidence

9. Types of impressions
Tool Marks
Shoe Prints
Tire Tracks
Bite Marks

10. Shoe Print Shoe prints can be left on multiple surfaces.
The first step with handling shoe print evidence is to photograph the print at multiple angles.

11. Shoe Print cont.
2-D: This type of impression is a flat deposit of dust and dirt.
Some impressions can be dusted with fingerprint powder to be photographed or lifted with tape or an electrostatic dust lifting process called “Pathfinder”.

13. Shoe Print cont.
3-D: prints can be made from shoe prints left in soft earth.
This type of impression is photographed first then casted
Casting involves the using dental stone (gypsum) or a similar substance to preserve the dimensional characteristics of the print.

14. Dust and dirt hardener firms up loose soil.

17. Shoe Print cont.
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.

19. Shoe Print cont.
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.

20. Footwear impressions are found at virtually every crime scene
Footwear impression evidence often provides an important link between the suspect and the crime scene.
Impressions left behind at the crime scene give the direction the suspect traveled while committing the crime.
This information may place the suspect at the crime scene or eliminate the suspect as having been there.

23. Types of impressions
Tool Marks
Shoe Prints
Tire Tracks
Bite Marks

24. Tire Tracks
Tire tracks 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.

25. Texas’s unsolved Phantom killer
Tire Tracks Cont.
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.
Texas’s unsolved Phantom killer

26. Tire Tracks Cont. Features to analyze: Tread pattern
Width & depth of the tread pattern
Unique characteristics due to the wear pattern or defects

27. Types of impressions
Tool Marks
Shoe Prints
Tire Tracks
Bite Marks

28. Forensic anthropologist Bill Bass, left, and his co-author, Jon Jefferson, examine a decaying corpse on the Body Farm.
Bite Marks
Human bite marks on skin, Styrofoam cups, gum or food can be helpful in murder and rape cases
Dental records including x-rays can also provide useful information, especially when attempting to identify a victim.

29. 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)

33. Types of impressions
Tool Marks
Shoe Prints
Tire Tracks
Bite Marks

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36. References
Saferstein, Richard. Criminalistics an introduction to forensic science. Upper Saddle River, N.J: Prentice Hall, Print.
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