1. Tool Marks and Impressions

2. Tool Mark
Any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.
Usually found at burglary scenes or scenes of forced entry

3. Comparing Tool Marks
Indented impression is left on the frame of a door or window as a result of prying with a screwdriver or crowbar
Close examination can reveal class characteristics or the size and shape of the tool
Usually can’t connect the marks to one tool unless there are random nicks or breaks that the tool has acquired

4. The edges of a pry bar, chisel, screwdriver, knife or cutting tool display microscopic irregularities that look like ridges and valleys
Left as a result of the machining process that is used to cut and finish tools
Damage and wear of the tool can also make imperfections
The variety of patterns among these tools makes it highly unlikely that any two will be identical
We can use these imperfections to identify individual tools

5. When a tool is scraped against a softer surface it may cut a series of striated lines that reflect the pattern of the tool’s edge
Compared using a comparison microscope with test tool marks made by the suspected weapon

6. Problems with Tool Mark Comparisons
Difficult to duplicate the tool mark left at the crime scene in the laboratory
Must make test tool marks at various angles and at different pressures

7. Collecting Tool Mark Evidence
Then entire object or part of the object bearing the tool mark should be submitted to the laboratory as evidence
When you can’t remove the tool mark from a crime scene you resort to taking a picture of it and make a cast of the mark
Liquid silicone is the best material to use for casting
A lot of detail can be lost when you are forced to use a photograph and a cast

8. Never attempt to fit the suspect tool into the tool mark this could alter the mark and question the integrity of the evidence
Suspect tool and mark are packaged in separate containers to keep from destroying their individual characteristics
Can be trace evidence like paint chips on the tool or impression
Must be careful when handling and packaging the evidence so you don’t lose any potential trace evidence

9. Impressions Can be a shoe, tire, or fabric impression
Preserving impressions
Impression is photographed first from the top and at various angles and in relation to the crime scene
Lifting impressions
When an impression is found on a surface that cannot be submitted to the laboratory we can lift the impression

10. Lifting Impressions
Place a lifting material over entire impression and use a fingerprint roller to eliminate any air pockets before lifting the impressions
Can use a portable electrostatic lifting device

11. Portable Electrostatic Lifting Device Continued . . .
Place a sheet of mylar film on top of impression and film is pressed against it with a roller
High voltage electrode of the electrostatic unit is placed in contact with the film and the unit’s earth electrodes are placed against a metal plate
Charge difference develops between the mylar film and the surface below the impression so the impression is attached to the lifting film

12. Electrostatic Lifting Film

13. Electrostatic Lifting Device

14. Casting Impressions
Shoe and tire marks impressed into the earth are best preserved by photographs or casting
Class I dental stone is the best material to use for casting
Cast has to air dry for 24 to 48 hours before it is shipped to the forensics lab

15. Casting Footwear Impression Evidence
                                                                                                                                                                               (Fig. 7)
                                                                                                                                                                               (Fig. 8)
Pouring Procedure
Place a form around the impression, if needed (Fig. 8) Pour the mixture onto the large spoon or stirring stick while holding the spoon or stick to the side of the impression. (Fig. 9,10) Allow the impression to dry a minimum of 30 minutes. Pertinent information, case number, date, time, location, etc. can be written on the cast after it is dry. (Fig. 16)
Casting Footwear Impression Evidence

17. Carefully remove the form from the cast. (Fig
Carefully remove the form from the cast. (Fig. 11) The cast must be carefully lifted. (Fig. 12) Place a knife one inch from the form and stick it directly into the ground under the cast. Gently pry upwards. This should allow the cast to break free cleanly from the surface.
                                                                                                                                                                               (Fig. 11)
                                                                                                                                                                               (Fig. 12)
Carefully remove the form from the cast. (Fig. 11) The cast must be carefully lifted. (Fig. 12) Place a knife one inch from the form and stick it directly into the ground under the cast. Gently pry upwards. This should allow the cast to break free cleanly from the surface.

18. Do not clean the cast until has been allowed to dry 24-48 hours. (Fig
Do not clean the cast until has been allowed to dry hours. (Fig. 13) Package the cast in a box or other porous packaging material. Package it securely to ensure that it is not broken during transport. Do not package a cast in plastic.

19. Pertinent information, case number, date, time, location, etc
Pertinent information, case number, date, time, location, etc. can be written on the cast after it is dry.

20. Comparing Impressions
Only possible when an item suspected of making that impression is recovered
Test impressions may be made for comparison
Look for class characteristics: Size, shape and design
Tell you if the impression was made by a particular shoe, tire or garment
Then look for individual characteristics: wears, cuts, gouges, or other damage
Can narrow down the impression to one source

21. SICAR Shoeprint Image Capture and Retrieval Shoeprint database
Searches known and unknown footwear files for comparison against footwear specimens
Can tell you the type of shoe
Also compares shoe print to suspect shoe prints from other crimes to see if they are a match

22. Bite marks
Human bite mark impressions on foodstuff and skin is another type of impression that can be used for comparison