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 Bodziak, William J. Shoe and Tire Impression Evidence. FBI Law Enforcement
Bulletin. Vol 53 No 7 (July 1984). p 2-12.
Abstract: Impression evidence can be overlooked or destroyed by
a hasty or disorganized search. Measure should be taken to locate, preserve,
and properly collect this evidence for laboratory analysis. The first law
enforcement officer, investigator, or technician on the scene should secure
it.
When examining the scene, investigators should pay particular attention
to tire and shoe impressions in areas of ingress, egress, and access where
they likely will have traveled. To locate impressions that may not be easily
seen on hard surfaces, thurn off the lights and direct a single strong beam
at a low angle. This will often illuminate dust impressions. When located,
impressions should be protected until they can be photographed and cast.
All impressions, even if they appear "worthless" should be retrieved
for evaluation.
Photograph impressions first in high-quality closeups from directly overtop
the impressions at a distance of 2 to 3 feet. These can provide greater
detail than a cast. The author recommends using a large size negative format,
fine-grained slow speed black and white film, a tripod, a ruler or scale
next to the impression, and proper oblique lighting at least three feet
away. Several photographs with the light at different angles should be taken.
Take care to correct for reflected light by adjusting the f-stop.
To cast an impression after photographing, remove debris that is NOT
part of the impression. Erect a form around, but well away from, the impression.
Class I dental stone is recommended as the medium with plaster of paris
as a substitute. Prepare the dental stone with the proper water mixture,
add dental stone until it ìcones upî in the center. Allow to
stand for a minute or two so the stone will settle in, then stir until the
consistence of thin pancake batter is reached. Pour the mixture over a spoon
away from the impression and allow it to flow evenly over the impression.
After 30 minutes of hardening, the cast can be removed. Do not clean the
cast. Allow to air dry 24-48 hours. If casting an impression in snow with
dental stone, stir in a small amount of snow or ice to lower the temperature
of the dental stone and make the consistency slightly more viscous so it
will not pass through the snow. "Snow print wax" can also be used
in snow.
Hard surface impressions (tile floors, counters, glass, concrete) made
with dust and residue should be photographed first as described above. Then
the item with the impression should be collected as evidence. If it cannot
be collected, the impression can be lifted with a footprint lift. Avoid
makeshift lifting materials like contact paper. Follow the directions on
the footprint lift package. Residue impressions may not transfer to a lift.
Make sure they are photographed and the item collected, if possible. Dusting
imprints with fingerprint powder is recommended only as a last resort.
Evidence shoould be packaged properly with description, type of examination
desired, item number, and any background information. Labs can make comparisons
to known footwear or tires and may be able to suggest the make and manufacturer
of the shoe or tire. Instructions for submitting specific types of evidence
are also included in the article.
For more information, contact:
Editor
FBI Law Enforcement Bulletin
FBI Academy
Madison Building, Room 209
Quantico, VA 22135
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