The first thing an attending officer should do once they have secured the scene is to preserve areas where the suspect could possibly have stepped. Many footwear impressions may not be immediately visible therefore entries and exits should be preserved for potential impressions. Traffic at the crime scene should be kept to an absolute minimum and where necessary the officer should use stepping plates or walk close to walls. If a footwear impression is located outside efforts should be taken to preserve the impression from the elements prior to suitable recovery.

Wherever possible the officer should submit the physical item bearing the footwear impression to the lab for recovery. Often times this is not possible so the officer must evaluate the impression and decide on the best course of action. The first decision what type of impression is present, this can generally be broken down into 3 categories – 3D, 2D and latent. Officers recovering footwear impressions are encouraging to spend some time looking for 2D or latent footwear impressions as these impressions are generally of much higher evidential value. Footwear impressions should always be photographed prior to attempts to recover.

3D footwear impressions in snow, sand, mud, dirt are one of the most visible evidence types especially in a climate such as Alaska’s. Before attempting to recovery any 3D impressions a series of photographs should be taken, these will complement any casts and document the impression in its original state, just in case the impression is destroyed during recovery. Before taking any photos any loose debris (that may have accumulated there after the impression was deposited) can be removed from the impression. Anything that is embedded in the impression, however loosely, should be left in place. Comprehensive photography of the crime scene including overall and mid-range photographs (including placards) should be taken. A close up photograph should then be taken from a 90° angle. The photo should ideally be taken using a tripod to ensure that it is perpendicular to the impression. The impression should fill the frame; this means the length of the footwear impression should fill the widest dimension on the screen of the camera. An L shaped scale should be placed next to and in the same plane as the impression. If the impression is 6” (15cm) down in fresh snow, you should dig a small trench 6” down next to the footwear impression (taking care not to cave the sidewall into the impression) and place the scale in it. Experiment with light from different angles to best illuminate the impression, around 10-20° usually works best. Take at least three photos using light from different sides as they will show different details within the impression. The placard number should be visible in the photograph.
If the impression is in snow/ice introducing contrast will help to get a better photo. To do this spray snow print wax or spray paint at a shallow angle around 6-10” (15-25cm) from the impression. A thin coat and oblique light will give the best results.

 

Once you have taken the necessary photographs move onto casting the impressions. Casts and photographs together is the best combination with 3D impressions. Photographs alone will only tell half of the story, likewise with just casts. They show different details to the forensic scientist. For impressions in snow it is recommended that you use snow print plaster. This comes in three pre weighed bags together with a mixing tub. Pour in pre chilled water up to the fill line. Sift in the powder and stir constantly for around 45secs-1min. When the mixture has the consistency of paint pour into the impression from a height of no more the 3” (7cm) (to avoid destroying the impression). The mixture sets very quickly and so to take care not to leave it too long when stirring and before pouring. Once the mixture is on the impression wait around 1min and lightly etch the item#, your initials and which direction north is into the back of the cast. After around 5mins you can check to see if the cast is ready to pulled up by gently tapping on it. If it feels hard and no longer wet it is ready. Gently slide your finger in under the cast and lift. If the impression is in very wet snow/ice or there is excess water accumulated in the bottom of the impression you can sift a little of the powder into it before casting. For all other 3D impressions dental stone is an adequate casting medium. Weigh out approximately 2lbs (1kg) into a zip lock bag. Pour in approximately 10oz (300ml) water and mix thoroughly making sure to get all pockets of powder out of the corners of the bag. When the mixture is the consistency of pancake batter cut one corner off the bag and gently pour the mixture into the impression for a height of less than 3”. After around 5-10mins the cast should be sufficiently dry to etch in the details as above. Dental stone casts take significantly longer to dry than snow print plaster 30mins-1hour depending on the weather. Once it is dry gently pull the cast by digging a small trench next to the impression and sliding your fingers in under the cast. To clean the cast it must be completely dry. This can take up to 24hours for dental stone. Run the cast under warm water and use a coarse brush to remove any excess mud or dirt. Before you reach the surface of the impression stop using the coarse brush. Small amounts of dirt can be removed at the laboratory. To submit the casts. Securely affix inside an evidence box using zip ties. Snow print plaster is not as strong as dental so use more zip ties than you think necessary and make sure not to pull them too tight.
Footwear impressions can occur on skin if a victim has been kicked or stamped on with sufficient force. Even if bruising has not developed yet sometimes an impression can be developed on the inside surface of the clothing. Take a photograph with a scale in the same plane as the impression. Often the full extent of the bruising does not develop for a few days after the incident so if possible re-photograph (including a scale) 2-3 days later. An alternative light source/Quaser may bring out details previously not visible.


 

Two dimensional impressions can be recovered from virtually any surface. For wet or residue impressions the main recovery tool is going to be a black gelatin lifter. Locate area of impression, photograph with scale and light as described above. Gently peel back acetate cover and wait a few moments for gel to return to natural size, starting at one end of the impression lay gel down, gently roll out air bubbles, peel up and re-photograph with oblique light and scale. Cover gel with acetate sheet and submit to lab.
In very dry conditions an electrostatic lifting apparatus (ESLA) often outperforms a gel lift. Cut an area of ESLA foil to fit the area of the impression. Lay foil over impression black side down. Place electrostatic lifter with ground points on grounding plate and charging point on film. Turn on and roll out using a wooden or rubber roller. Make sure not to touch foil or surrounding area while charging. Turn off ELSA. Leave for a few moments for charge to dissipate. Peel up foil and examine using oblique light. Photograph with scale and tape into clean flat box. Submit to lab. NB ESLA lifts are very fragile, exposure to dusty environments, physical contact and packaging in static inducing containers (plastic) while destroy the lift.
Impressions in suspected blood can be enhanced using a variety of chemicals depending on the surface they are left on. Please contact the lab to discuss enhancement/recovery. Please note that the most visible impressions are often not the best for analysis. Fainter impressions often reveal much more detail upon chemical enhancement.

Often the highest quality footwear impressions are the ones you cannot see initially. A thorough search of an area with an oblique light is the best way to determine if there may be an impression present.
If there are papers/envelopes/magazines/cardboard present that may have been stepped on by a suspect these can be collected and submitted where they will be enhanced using an electro static detection apparatus (ESDA). Entryways and harder surfaces can be speculatively searched using the ESLA device and up to 3ft sections of film as described above.

Every person who attends the crime scene should have an elimination footwear impression taken. This impression can be anything from a photograph of the sole design, an inkless pad (Identicator) impression or a piece of aluminum foil that is stepped into on a smooth soft surface. Each elimination print should have the identifiers of the person attached.

Can you tell what size shoe made a footwear impression?
Usually the answer to this question is no, for a number of reasons; distortion in the impression, only a partial impression recorded, problems with the scale in the impression, manufacturing size and mold variations. If you have a major case impression and finding out the size is paramount to your investigation please call the crime lab and we may be able to offer some assistance.

Can you tell someone's height from a footwear impression?
No, while there is a general correlation between foot length and height it's very difficult to do anything other than estimate and there are always exceptions to the rule.