FOOTWEAR AND TIRE TRACK EVIDENCE
| Casting methods | Two-dimensional impressions | Exemplars and standards |
| Collection and packaging | Evidence Officer procedure | Disposal |
Shoe and tire impressions are routinely present at crime scenes and are frequently overlooked by law enforcement personnel. In many instances the examination of these impressions can provide the investigator with valuable leads such as the type, make, and approximate size of the footwear or tire. If properly documented and collected, almost every impression left by a shoe or tire has value for forensic comparison to a suspected source.
Only a person with appropriate training should attempt to document or gather impression evidence.
Impression Methods
Photograph the impression with and without a scale device. The scale should be a two dimensional ruler (see figure 7).
Whenever possible, retrieve the original item containing the impression (e.g. paper, glass, flooring, door) for submission to the laboratory.
Lift or cast the impression when it is in soil, sand, or snow, or when it cannot be sent to the laboratory.
Photographs of the evidence should always be taken first before any attempt to collect it.
Photograph the general scene that contains the impression evidence.
Select a camera with a large negative format such as 35 mm or 4x5 inch.
Place the camera on a tripod with the camera directly over and perpendicular to the impression. Adjust the camera height so the impression and scale fill the frame. Use overlapping exposures to record elongated impressions (see figure 6).
Use side lighting at various angles and from various directions to illuminate tread design more clearly. This may require shading the camera setup from high, bright sunlight with a makeshift tent and access to a detachable flash unit.
Fine grain black and white or color film (ISO 125 or less) is preferred.
Three-dimensional impressions are those that have a significant depth to them, in addition to the length and width of the impression. Commonly, they may be found in soil, sand, or snow and the detail within the impression may vary according to the substrate. Casting is an effective method of collecting these types of impressions.
Dental stone or die stone should be used to cast footwear and tire tread impressions in soil and sand. Plaster of Paris is no longer recommended as an acceptable casting material. Dental stone can be obtained from local dental supply houses or forensic equipment supply catalogs.
Two (2) pounds of dental stone may be placed into an 8x12 inch Ziploc plastic bag; this amount will cast an average sized shoe impression. In preparation for use at crime scenes, numerous two-pound bags can be prepared and stored.
The following is the procedure for making a cast:
Retrieve a two-pound bag, add about 10 ounces of water, and thoroughly mix in the closed bag. The mixture should have the consistency of thin pancake batter. If needed, add more water or dental stone to create the correct consistency.
Open the bag and with the bag at ground level, carefully pour the mixture into or next to the impressions, allowing it to gently flow into it. Fill the impression completely so that the mixture overflows out of the impression.
When the cast is firm but still soft, scratch identifying marks on the exposed surface or write identifying marks with a permanent marker when the cast is dry.
Allow the cast to dry for a minimum of twenty minutes in warm weather, longer in cold, wet conditions.
Carefully lift the cast. Do not try to clean it; cleaning will occur in the laboratory.
Package the cast in a large brown paper bag or cardboard box (not plastic) and allow to dry for an additional 48 hours.
A two-dimensional impression is one where there is no significant depth to the impression. A thin deposit of dust, mud, blood, or other material from a shoe onto a hard surface may create these impressions.
Floors, glass, desktops, doors, paper items, etc. can retain a dust or residue impression at a scene. Some impressions may be clearly visible while others may be partially or totally latent.
Turning out all lights and shining a flashlight across the surface of interest can locate latent dust shoeprints. For example, to search for latent shoeprints on a vinyl floor, place the flashlight on the floor (or near it) and allow the long beam of light to shine across the floor.
Photograph the impressions, as described above, before collecting. See Figure 6.
Normally, the deputy will only try to collect impression evidence if it is on an item that cannot be retrieved from the scene and submitted to the laboratory.
Dust and residue impressions may be lifted with an electrostatic lifting device or gelatin lifter.
There may be several people who have legitimately walked into a crime scene. These include first responders, medical personnel, members of the crime scene team, funeral home personnel, or Medical Examiner’s Office personnel, individuals from the District Attorney’s Office, etc. Therefore, it can become difficult to differentiate between shoeprints that are evidence and those that result from crime scene processing.
Exemplars may be collected from people entering the crime scene in a number of ways. A good way to do this is have the person keeping the crime scene log require everybody entering the scene to give a shoeprint exemplar before proceeding into it. This may be accomplished by:
Taking a photograph of the shoe sole.
Having the person step onto a piece of aluminum foil, which is on a flat piece of cardboard (leaving a rough impression of the shoe sole).
Greasing the soles with a thin film of petroleum jelly and having the individual step onto a clean piece of paper. Dusting the grease print with fingerprint powder for visualization.
Shoes should be submitted to the laboratory as standards from all individuals thought to have left evidence shoe impressions at a crime scene.
Rather than submitting standard tires to the laboratory, exemplars may be made from them by inking the tire while it is on the vehicle and rolling it onto clean, white, heavy-stock paper.
You may also grease the tire with a thin film of petroleum jelly, roll it onto paper, and dust the resulting grease print with fingerprint powder as described above. For each tire you will need about 6 feet of paper, depending on the tire size.
Both methods work best when the vehicle is on a clean, smooth surface.
Whenever possible, collect the impression evidence and submit it to the laboratory.
Submit the photographs of the impression evidence to the laboratory.
Protect the impression evidence item so that the impression does not rub off.
A good way to protect flat impressions is to carefully secure them to a thin piece of cardboard or the bottom of a paper bag.
Complete the evidence tag and attach it to the packaging. Complete the property-evidence report.
Deliver items that need to be dried to the evidence processing area of the Forensic Science Unit; note the location on the property-evidence report.
All other items can be placed in an evidence locker; note the location on the property-evidence report.
Place the yellow and green copy of the property-evidence report in the basket in the evidence processing area.
STORAGE
Ensure proper packaging; refer to the example board in the evidence processing areas.
Place one barcode on the item and the corresponding barcode on the property receipt.
Place the item in a location best suited to the size of the article, and area specified by the evidence room guide.
Using the barcode reader, scan the location of the shelf, and then scan the barcode affixed to the item.
Place the item in chronological numerical order by case number.
Upon disposition, request authorization from investigating officer.
Upon expiration of statute of limitations, request authorization from the investigating officer.
Revised 11/05/03