1. FOOTWEAR AND TIRE TRACK EVIDENCE
Collection, Preservation and Analysis

2. Impression Evidence
Objects or materials which have retained the characteristics of other objects which have been impressed in them

3. We’re looking for…. Visible impressions
Latent impressions (oblique light)
Electrostatic Dust Print Lifter

4. Area of emphasis Point of entry Area where crime occurred
Route through scene - if possible to determine
Point of exit - include exterior
Around other detected impressions

5. Preservation of footwear impression evidence
Photography
Casting
Electrostatic Dust Print Lifter
Dusting & lifting
A combination of the above

6. Photography Proper technique is essential
If not done properly it will greatly limit what an examiner can determine
Examination quality photos vs. general photos
Basic photographic equipment and some practice are needed

7. Common mistakes
The scale needs to be on the same plane as the impression
Focus on the impression
Be over the impression at 90 degrees
Use a tripod to stabilize the camera
Use a cable release or self timer

8. Tips & Techniques Detach the flash from the camera
Vary the lighting angle by about 10 degrees until you have completed a 180 degree arc
Drape a black cloth around the impression or tripod to eliminate outside lighting
Can also use a large piece of cardboard to shadow the impression – in place of the cloth
ALWAYS use a ruler for the scale

9. Depth of Field

10. Distinguish between multiple impressions

11. Photograph with scale

12. Invert a camera on a tripod for stability & to be over at 90 degrees

13. Shade the impression & vary the flash angle

14. Photograph with a scale

15. Spray with Snow Print wax & re-photograph

16. Snow Print Wax Used prior to casting
Highlights detail in the impression
Acts as a mold and release agent for the casting material
Keep sunlight from striking the impression & the wax

17. Casting Is done AFTER photos have been taken
Photos & casts supplement each other
Casts can recovered three dimensional detail which cannot be captured with a photo

18. Dental stone Easier to clean Does not scratch if brushed
Does not require reinforcement or a dam
Easier to mix/use
Finer texture
No heat build up

19. Dental stone Two pounds of stone and about 12 ounces of water
The consistency of thin pancake batter

20. Cast away….

21. Add water SLOWLY to the bag

22. Knead the water & dental stone in the bag

23. To dam or not to dam?

24. Pour slowly from the bag over an inverted spoon

25. Jiggle (scientific term) it to work it in to the impression

26. Mark it when it begins to harden

27. Castings forms Poured into a form
Best to use form to add thickness to the cast
Prevents the edges from being thin and breaking easier
Pour over an inverted spoon to prevent washing the impression out

28. “Fixing” 3-D impressions in dirt
Dust & dirt hardener
Costs a lot
Hair spray
Cheaper to buy
Does the same thing

29. Enhancing for photos and release agent for casts

30. Collecting two dimensional impressions
If the impression can be easily taken from the scene…take it
The development and lifting techniques are the same as those used for fingerprints

31. Electrostatic Dust Print Lifter
Will only work on dry origin impressions
If the impression was wet originally it will not work
If the impression does not lift it is not destroyed

32. Dust Print Lifts An electrical charge is applied to the lifting film
The dust is then attracted to the film
Oblique (low angle) light is then used to see the image lifted

33. Gel Lifters The impression is developed using powder or chemicals
The gel lifter is applied to the developed impression
The lifter remains on the impression for minutes

34. Gel Lifters The impression becomes embedded in the gelatin layer
The impression is reversed when viewed
The lifted impression must be photographed ASAP

35. Accidental characteristics
Random cuts, gouges or abrasions made to the out sole during the wearing of the shoe
As the shoe is worn it develops unique characteristics

36. Temporary accidental characteristics
Foreign debris or substances become attached to the out sole
These can change over time
Because of that they have greater significance

37. Manufacturing methods
An examiner must have knowledge of manufacturing methods
It helps with examination and being able to attribute characteristics to wear

38. Stippling The stippling is added by hand stamping
Stippling pattern will be unique to the mold
Can also be done using an acid etch process – this will be unique to the mold

39. Footwear database
FBI has a collection of outsole designs in a database
An image (jpeg) can be submitted electronically to:
A written request will then have to be submitted (via FAX) providing the case #, victim, suspect info. and brief case facts
The database contains images voluntarily submitted by manufacturers

40. Scene impression & search result

41. Tire Evidence
Collected and preserved using the same methods as footwear evidence
Exhibits will be bigger – evaluation of the scene impressions is important
Analysis will require more time to perform

42. Data base
RCMP and Michigan State Police maintain a data base of tire and wheel information
By taking stance (width) and wheel base measurements a “candidate” list can be generated
Careful measurements are critical – the better the measurement the shorter the list

43. Tire Evidence
Stance measurements should be made to the nearest 1/8th inch
Tire size change will not alter this – changing the wheels will

44. Tire Evidence Turning diameter can also be used
Chord and middle ordinate measurement
How do you know the wheels are turned to the steering lock?

45. Noise Treatment
The size of the design elements on the edge of the tire vary in size
This keeps the tire less tonal and reduces overall noise
This can be a significant clue for the examiner
Helps get the examiner down to several small areas of the tire instead of the whole thing

46. Test impressions Photograph the tires on the vehicle
Note the size and make of each tire and it’s position
In most cases it is best to let the person doing the examination take the test impression
Test impressions can be done several different ways and it is best to let the examiner decide