FOOTWEAR AND TIRE TRACK EVIDENCE Collection, Preservation and Analysis

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

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

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

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

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

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

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

Depth of Field

Distinguish between multiple impressions

Photograph with scale

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

Shade the impression & vary the flash angle

Photograph with a scale

Spray with Snow Print wax & re-photograph

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

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

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

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

Cast away….

Add water SLOWLY to the bag

Knead the water & dental stone in the bag

To dam or not to dam?

Pour slowly from the bag over an inverted spoon

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

Mark it when it begins to harden

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

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

Enhancing for photos and release agent for casts

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

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

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

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 10-15 minutes

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

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

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

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

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

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

Scene impression & search result

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

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

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

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?

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

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