Many latent footwear impressions can be located with the oblique lighting technique. Once found they can be difficult to photograph, but latent fingerprint powders can be used to build contrast for easy photography. This procedure is performed in the same manner as if you were dusting for latent fingerprints. Once the prints have been developed and photographed, the recovery process is the same using fingerprint lifting tapes and suitable contrast backgrounds to place the lift on. Never cover an impression with tape to reserve it until after the completion of the photographs. The tape will only obliterate the print and make subsequent enhancement difficult. Place the tape over the impression only after all other methods of enhancement have been exhausted. Make sure the footwear evidence was not placed in dust, as there may be more suitable methods of collection.
Since 1981, an excellent recovery method for visible and invisible footwear evidence has been widely used around the world and has resulted in footwear identifications. This technology is called the electrostatic dust lifter.
The system has a high voltage electrostatic charge that creates a charge on a piece of lifting film and causes some of the dust or residue particles to transfer to the underside of the lifting film. The system works on a wide variety of surfaces including, floors, doors, countertops, chairs, fabric, metal, carpet tile, newspapers, bodies, tar and many others. The quality of the print is dependent upon the type of surface it is deposited on. No matter what the detail is that is recovered the crime scene investigator should always turn the print over to the examiner for examination.
There are four basic methods of recording footwear impressions at the crime scene.
The crime scene investigator, when collecting evidence, should “use known methods in the best possible way to develop the impression to its fullest potential.”
Crime Scene Footwear Evidence
Footwear evidence can be found in two forms, impressions and prints. The impression is normally described as a three-dimensional impression, such as an impression in mud or a soft material; and the print is described as a print made on a solid surface by dust, powder, or a similar medium.
Footwear evidence, as well latent fingerprint evidence, is classified into three categories of crime scene prints:
- Visible Prints
- Plastic Prints
- Latent Prints
The Visible Prints: A visible print occurs when the footwear steps into a foreign substance and is contaminated by it, and then comes in contact with a clean surface and is pressed onto that surface. This print can be visibly seen by the naked eye without any other aids.
The most common visible prints are prints left on a contrasting surface, such as a kitchen floor. A variety of substances, such as blood, grease, oil, or water will leave contrasting prints. This type of print must be photographed, prior to any other methods being used. An electrostatic dust lifter can also be utilized when the evidence is in dust.
The Plastic Prints: Plastic prints are impressions that occur when the footwear steps into a soft surface, such as deep mud, snow, wet sand, or dirt creating a three-dimensional impression. This type of impression should be photographed and then cast. These types of impressions are three-dimensional because they allow the examiner to see length, width, and depth.
The Latent Prints: Latent prints are the most overlooked print and are generally found on smooth surfaces. They can be developed the same way latent fingerprints are. This type of print needs a variety of powders, chemicals and even forensic light sources to make it visible in order to properly be collected. In most cases these prints should also be photographed prior to any recovery process.