Evidence Collection Handbook - SHOE PRINT and TIRE TREAD EVIDENCE

Evidence which falls within this category includes shoes, tires, plaster casts, prints, and photographs of shoe or tire prints and impressions. As shoes and tires are used, individual characteristics such as nicks, cuts, and wear patterns develop. These characteristics may show up in prints and impressions and can be compared to a suspect's shoes or tires. Shoe and tire evidence is submitted to the laboratory's Firearms unit and is examined for like individual and class characteristics.

Shoe or tire "prints" are of a two-dimensional nature, having length and width. These are commonly found on pieces of paper as dust prints or can be made by tracking through mediums such as blood, water, oil, and dirt.

Shoe or tire "impressions" are three-dimensional in nature, having length, width, and height.  This type of evidence is usually found in soil and is collected and reserved by the use of a plaster cast.

Value.

One of the most commonly overlooked types of physical evidence is the perpetrator's "tracks". Evidence of this type, whether made by shoes or tires, can link a suspect directly to the crime scene, and can be used to rule out a suspect or can be used to identify a victim.

Shoes and/or tires, when compared to a print or impression, can be identified to the exclusion of all others if like individual and class characteristics are found.

Collection of Evidence.

These techniques are brief and should be practiced before any attempt is made at actually collecting the physical evidence.

Photography.

1. Any prints or impressions found should be photographed prior to any collection attempts. The camera should be perpendicular to and directly over the print or impression. One photograph should be taken of the evidence as it is, one should be taken with a ruler laid to the side so the photograph can be enlarged to a one-to-one scale, and one additional photo should be taken showing the evidence's relationship to its surroundings.

2. Light should be directed toward the print or impression from the side to prevent the detail from being washed out.

3. All negatives should be submitted in addition to photographs.

4. Photographs should always be used as a backup and not a substitute for the collection of the actual evidence.

Prints.

1. It is preferred that the original print be collected if at all possible. If it is not practical to collect the object that the print is on, then a lift can possibly be made. Always photograph the print prior to an attempt to lift the print. Then take wide fingerprint tape and cover the entire print. Overlap several pieces of tape as necessary to cover the entire print. The lifted tape then can be placed onto a piece of white paper.

2. Submit any partial prints found. An identification can possibly be made on a very small portion of a whole print.

Impressions.

1. Make a test cast!

2. After photographing the impression, remove any loose debris that may have fallen or was blown into the impression and photograph again. Always take a photograph with a ruler next to the impression.

3. Use a cardboard box to protect the impression if a cast cannot be made immediately.

4. Make a dam around the impression to hold the plaster. Garden edging makes an excellent dam.

5. If the soil is of a loose sandy type, use shellac or hair spray to firm the soil prior to pouring in the cast. Be careful in directing the spray of the "fixer" so that it does not blow away the impression. Spray in a way that will let the "fixer" gently floats down into the impression.

6. Dental Stone or Die Stone is commonly used as a casting medium. Die Stone or Dental Stone is preferred over Plaster of Paris due to its hardness and faster setting time.

7. Mix the casting medium according to the instructions provided with the material being used. Dental stone is usually prepared by mixing two (2) pounds of powder with 12 ounces of water in a large zip lock plastic bag. The ideal mixture should be pancake batter consistency, not thick nor watery.

8. Break the mixture's fall by pouring onto a spatula. Allow the plaster to fill the entire impression. No reinforcing support is needed if Dental Stone is used.

9. Make several casts of a long tire impression.

10. The cast should be allowed to set for at least an hour before attempting removal. After the cast has partially set, scratch the exhibit number, case number, and your initials into the back of the cast.

11. Do not clean the cast yourself. The lab examiner will clean it.

Shipment

Prints.

All original prints should be placed in a shallow box or brown paper sack and secured. Do not place anything on top of the print. Seal the box to prevent anything from falling onto the exhibit.

Always mark the box or sack with all pertinent information.

Casts.

Place each cast individually in a box and cushion with newspapers or place in brown paper sack. Seal the box and mark with all pertinent information.

Shoes.

Attach an evidence tag to each shoe and place each shoe in a separate paper bag. Also mark the bag.

Do not remove any dirt or foreign material from the shoe prior to packaging.

Tires.

Attach an evidence tag to each tire and transport.

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