Processing wet two dimensional footwear
impressions on concrete
By Donald A. Hayden
PURPOSE: The purpose of this paper is to document a method of processing wet two dimensional footwear impressions on concrete.
BACKGROUND: Footwear impressions are present at virtually every crime scene, however are frequently overlooked. We’ve all been to a crime scene and discovered two dimensional grease footwear impressions. Many methods of lifting those grease impressions have been developed, from using gel lifters to use of dental stone. That’s been great for patent impressions, but what about wet, fugitive impressions?
Imagine for a moment, you respond to a warehouse and observe that the warehouse has apparently been burglarized and a cursory review reveals that several items appear to be missing. Your initial check reveals that there are numerous wet “boot prints” visible on the concrete floor. Water evaporates fairly quickly, so all you can do is hastily photograph the scene right? Well, not quite. As is demonstrated in the following sequence of photographs, those wet prints can be processed in a manner that makes them ideal for casting and collection.
MATERIALS: The materials used in this process as readily available anywhere. They consist of: Black magnetic powder; a Magnabrush, a photography system which must consist of camera, tripod and scale; and casting material.
Step 1: Your initial actions must be to photograph the impression with and without scale.
Step 2: After you photo-document the impression, using magnetic powder, charge your Magnabrush. Then gently “paint” the magnetic powder over your impression, using great care to barely touch the impression with the powder. This is somewhat different than normal magnetic powder application, as you must not allow powder to drop into the impression or you will not likely get a useable impression.
Step 3: When you are happy with the detail you have on your impression, re-photograph the impression, with and without scale.
Step 4: Using dental stone casting compound, create a form around your impression. A piece of paper folded over several times, and taped to the surface works well. (Hint: Place a tongue depressor or a pair of scissors under the edge, to allow easier lifting of the cast). Tape the form down on all sides creating a good seal.
Step 5: Prepare your dental stone casting mixture to about the consistency of pancake batter and pour it into the cast (note: This mixture should be slightly more watery than normal). Care must be taken to allow the mixture to land on an area that does not contain your magnetic powder. Rather allow the mixture to “flow” over the cast and fill slowly.
Step 6: Once the cast is completely covered, mix ample dental stone to make the cast not less than one inch thick.
Step 7: When you have completed pouring, mark your cast in compliance with agency directives.
Step 8: Allow cast to airdry for an extended period of time (usually a couple hours) and it will pop right up with a useful impression the lab will be able to conduct examinations of.
DISCUSSION: There are many variations of this theme available to the crime scene investigator. We have used this collection method on both sealed and unsealed concrete; tile floors; and wooden stairs. Our best results were on anything that was sealed, such as sealed concrete or vinyl, however all surfaces revealed useful prints. One particular challenge we discovered in our efforts was the evaporation of the print when in direct sunlight. For that reason, speed is of critical import. Additionally, on unsealed concrete, the water will spread over the impression and in a span of several minutes; the print can be rendered useless. Again, a sense of urgency can override this problem.
SUMMARY: Although many methods of documentation and collection of impression evidence have been developed, use of “low-tech” methods, such as magnetic powder and casting materials, makes obtaining footwear from a crime scene an option even at departments with limited budgets.
Donald A. Hayden
Chief, Physical Evidence Branch