Reference Citation: Schiro, G. Shoeprint Evidence - Trampled Underfoot. Southern Lawman Magazine, Fall 1999
George Schiro, MS, F-ABC
Shoeprint evidence is one of the best types of evidence for placing a person at a crime scene. As my supervisor Jim Chirchman is fond of saying, “No one ever levitates at a crime scene, the perpetrator has to walk in and walk out.” Unfortunately, in most instances, shoeprint evidence is also one of the most neglected and abused types of evidence. Many a crime scene shoeprint has been trampled underfoot, usually unintentionally and long before the crime scene investigators and the detectives have even arrived. Even though the shoeprints may have been trampled upon, they should not be abandoned. By carefully eliminating all of the other non-suspect shoeprints that might be at the crime scene, the perpetrator’s shoeprints may still be identifiable. Just like a fingerprint, an entire shoeprint is not necessary to make an identification. If enough individualizing characteristics are present, a one square inch area of a shoeprint could be enough to positively identify it as having been made by the suspect’s shoe.
Shoeprint identification is an old, well established form of identification. The first recorded use of shoeprint evidence in a criminal case took place in 1786. The theory behind shoeprint identification is relatively simple. When a new shoe is purchased, the shoe sole is usually unmarred. As someone puts on the shoe and begins to walk, the shoe sole becomes randomly marred by pebbles, glass, nails, abrasive surfaces, etc. The nature of this random marring imparts individuality to this shoe sole. As more random cuts, gouges, nicks, or worn areas accumulate on the sole, the shoe sole becomes more unique. If this person were to commit a crime, he or she could leave a detailed shoeprint impression at the crime scene. If properly documented, collected, enhanced and/or preserved, this shoeprint impression could be retained for many years. If the shoe’s original owner becomes a suspect in the crime, his or her shoes could be examined and compared to the evidentiary shoeprint. The areas that would absolutely link the shoe to the print are the shoe defects caused by the random action of these marring agents. These defects are referred to as individualizing characteristics.
Crime scene shoeprints may also be present without sufficient individualizing characteristics to absolutely match to a set of reference shoes. The cause of this is usually a direct result of the shoe sole’s condition and its interaction with the contacted surface. Although these shoeprints may not absolutely match a set of reference shoes, these shoeprints could provide valuable class characteristic information. Class characteristics are characteristics shared by a limited group of items. Class characteristics usually refer to the shoe’s size and the pattern of the shoe sole. These characteristics will be shared by all other shoes manufactured with the same size and pattern. In many cases, class characteristics of a crime scene shoeprint can be used for rapid elimination of reference footwear if the footwear is a different size or has a different pattern. If the class characteristics of the shoeprint and the reference footwear are the same, then further study of that footwear and print for individualizing characteristics may be warranted.
In order to maximize the amount of available information from the shoeprints and the other evidence, the crime scene must be properly protected and documented. Much of that information has appeared in my columns in the Fall 1998, Winter 1998, and Spring 1999 issues of SLM; however, some of it bears repeating. The first critical step in processing a crime scene is protection of the crime scene beginning with the arrival of the first police officer at the scene and ending when the scene is released from police custody. While protection of the crime scene and evidence is very important, it takes a back seat to the officer’s safety and the safety of others. The officer’s first responsibility is his or her own safety. The officer’s second responsibility is the safety of any others who may be in danger. The law enforcement agent must take all measures necessary to ensure that these responsibilities are carried out, even if these actions result in the compromise of some evidence.
Although an officer should take any necessary action, he or she should also strive to expand his or her knowledge about evidence and its value in an investigation. Through training, reading, and education on the application, value, and limitations of physical evidence, an officer may be more aware of his or her actions as a first responding officer and the impact of these actions on the crime scene evidence. The information about his or her actions can then be passed on to the detectives or crime scene investigators handling the case. The first officer should make mental or written notes as practical in each situation about the condition of the scene upon the officer's arrival and after the scene has been stabilized.
Once the scene has been stabilized, any areas that may yield valuable evidence (driveways, surrounding yards, pathways, etc.) should be roped off to prevent unauthorized people from entering the area and potentially contaminating it. Investigators and other necessary personnel should be contacted and dispatched to the scene. A command post should be set up away from the crime scene for eating, smoking, drinking, etc. Before the detectives and crime scene investigators begin the scene examination, they should gather as much information as possible about the scene to prevent destruction of valuable and/or fragile evidence such as shoeprints.
The examination of the scene will usually begin with a walk through of the scene to note the location of evidence and mentally outline the examination of the scene. The first place the investigators should examine is the ground so they don’t trample on and obliterate any existing shoeprints. If any evidence is observed, then a highly visible marker should be placed at the location as a warning not to step on the item of interest. The investigator must take his or her time when looking for shoeprints. This may require a search on “hands and knees” and may require a variety of lighting conditions to visualize the shoeprints. Oblique lighting and angled lighting with a strong flashlight are particularly useful for finding latent, or not readily visible, shoeprints. The investigators should use oblique lighting on an area of the floor and make sure that section of floor is clear or the evidence is clearly marked before proceeding to the next area. When the walk-through is completed, the scene should then be documented by using notes, videotape, photographs, and sketches.
Almost any type of camera with interchangeable lenses and a format of 35mm or larger can be used for crime scene photography. The lenses should include a 28mm wide angle lens, a normal 55mm lens, and a lens with macro capabilities (1:4 or better). The flash unit used with the camera should not be fixed to the camera. It should be able to function at various angles and distances from the camera. This allows lighting of certain areas to provide maximum contrast, placing the flash in hard to reach areas, and reducing flash wash out that can render a photographed item invisible. A Polaroid camera should also be handy for instant photographs that may aid in the investigation. For example, an instant photograph of a shoeprint found at a crime scene can be provided to investigators who are running a search warrant on a suspect's residence. The photo will show them the type of shoe for which they are searching.
The best medium for documenting shoeprint evidence is film photography. This will be the case until digital cameras can duplicate the resolution power of film. For shoeprint photography, plenty of fine grain color print film (25-100 ISO) should be used. Black and white film is also ideal for shoeprint documentation because it has a fine grain structure and can be manipulated in the darkroom to produce high contrast photos. 35mm cameras produce excellent results, but larger format cameras will provide excellent detail.
Actual size, or one-to-one, photographs are absolutely essential for documenting shoeprints. For actual size photography, a cable release, an angle finder, a “right angle” ruler, such as an ABFO No. 2 ruler or a “Bureau” scale, and a clear acetate sheet on which a one centimeter or 1/2 inch grid is printed may also be necessary. Coins, paper clips, pens, etc. are not suitable scales for one-to-one photography. Photographs should be taken with a scale and without a scale. The film plane must also be parallel to the shoeprint. If the ground is level, then a level can be used to make the camera back level also. If the shoeprint is on an incline, then an angle finder can be used to find the angle of the incline. The camera back should be adjusted to the same angle as the incline. The flash or light source should be angled or oblique. Because film is cheap and an investigator usually only has one opportunity to document the evidence, the crime scene investigator should bracket all scaled one-to-one exposures and take many photos to ensure that the photographs will be properly exposed. Bracketing is photography in which the camera’s f-stop is varied to change exposure between photos.
After the scaled photographs are taken, the investigator may want to use the clear acetate grid overlay to take more photos. This grid will demonstrate distortion due to lens aberration, if the camera was off-center, or if the camera’s film plane was not parallel to the impression. The grid will also allow documentation of shoeprints on curved surfaces and on surfaces where the camera cannot be positioned directly over the print. The grid must cover the impression, and be flush against the print. The flash must be held at an angle, and the overhead lights must be blocked to avoid glare. Once again, several bracketed exposures should be taken. The grid must be moved slightly and the process repeated so that no individualizing characteristics are covered by the grid. Because the grid has fixed measurements, then any distortions in the photo will be readily apparent through changes in measurement on the photographed grid.
Once these photographs are taken, the two-dimensional shoeprints can be enhanced. Enhancement may include dusting the shoeprint with fingerprint powder, developing latent bloody shoeprints, development of metallic ions in the print, or developing oily prints. After enhancement, the prints will be photographed using the same techniques and steps described above, except that oblique lighting may not be necessary. If the print is readily visible after treatment, then an angled flash should be sufficient to prevent any flash washout. As with the first set of photographs, these one-to-one photos should also be bracketed to find the ones with the best exposure.
Three dimensional shoeprints are shoeprint impressions retained in a deformable material which may remain deformable or may harden. For example, a shoeprint in mud may remain deformable if kept moist or it may harden if it dries out. The same set-up and rules used in photographing two dimensional prints apply to documenting three dimensional prints except that instead of using oblique lighting, the flash will provide angled lighting from 10- 45°. If the print is in direct sunlight, then the print should be shaded from the sunlight so the print can interact with the angled lighting provided by the flash unit. As mentioned above, a flashlight can first be used to determine the optimal lighting angle. The angled lighting is used to prevent flash washout and to bring out greater detail in the prints. If possible, the ruler on the one-to-one photos should be in the same plane as the prints. Some shoeprint examiners even recommend digging a small trench next to the shoeprint for the ruler. This should only be done if it does not disturb the print. The bracketing rule and the 100° rotation rule also apply to these one-to-one photos. The clear acetate grid is probably not needed for the three dimensional prints. Once the documentation is complete, the shoeprints can be enhanced and/or collected.
In most cases a shoeprint is never really collected. Usually a cast is made of a three dimensional shoeprint or a lift of a two dimensional shoeprint, either electrostaticly or through dusting techniques, is collected. The only time the shoeprint is actually collected is when it can be removed from the scene without disturbing the print and it is never removed without first thoroughly documenting the shoeprint. Whenever possible, the crime scene investigator should not rely on documentation alone. Because they complement each other, the documentation and the cast or lift should be submitted to the crime lab for evaluation.
For three dimensional prints, the casting material of choice is Class I or Type I dental stone. While other materials have been and can be used, dental stone lasts longer, is less expensive, is durable once hardened, and is not messy to use. Dental stone, which should not be confused with dental plaster, is available in bulk amounts from most dental supply houses. For most three dimensional prints, two pounds of dental stone will suffice. Slightly larger amounts may be necessary for deeper impressions. The easiest, least messy way to use dental stone is to pre-measure about two pounds of dental stone in a zip-lock bag. Several of these zip-lock bags can be transported to crime scenes. Dental stone can even be used to cast shoeprints underwater.
Casting shoeprints in snow can be quite difficult because snow has a tendency to melt during the casting process. Several materials for casting and/or enhancing snow shoeprints are available, such as Snow Print Wax; sandable, gray auto primer; melted sulfur; and melted paraffin. Some people have more success with certain materials than others. The most important factors are probably the person making the cast, his or her familiarity with the casting material, the climate, and his or her experience.
Sandable gray auto primer combined with chilled dental stone is one method available for snow shoeprints. After the initial documentation photos have been taken, the shoeprint to be treated should be blocked from direct sunlight. The print is lightly sprayed at an angle with gray auto primer to highlight the details of the print. The spray can should be far enough away from the print so the aerosol does not disturb the print details. After lightly spraying the print, the photo sequence is repeated. After the photos are completed, 10-12 ounces of a 5-10% solution of potassium sulfate in water mixed with snow is added to the dental stone. It is mixed and added to the shoeprint as described above. The potassium sulfate lowers the freezing point of the water and accelerates the setting of the dental stone. Once hardened, the cast can be removed and handled as described above.
In addition to collecting three dimensional casts, two dimensional shoeprints can be “collected.” One relatively simple method of collecting dry prints in which dust from the shoe has adhered to a surface or where the shoe has displaced dust from a surface is to use an electrostatic dustprint lifter. A commercially available dustprint lifter can be bought or one can be adapted from an electric “stun-gun” or any other source that will impart a static electricity charge to a piece of black lifting film. After the obligatory photos are taken, a piece of black lifting film is placed over the print. An electric charge is applied to the film causing it to adhere to the surface. A roller is used to smooth out any air bubbles that are present. The electric charge is turned off and the film is allowed to relax. The film is then picked up with the dustprint impression adhering to it. The film should be taped into a box to prevent the print from being disturbed. The box can then be sealed, labeled and submitted to the lab.
In order to collect shoeprints made from the residue accumulated on the shoe sole or from prints containing a slight amount of moisture, the print may have to be dusted and lifted like a fingerprint. If a print is obviously wet, it should be air dried before attempting to dust it, otherwise valuable detail may be lost in the dusting process. Just like a fingerprint, the print can be dusted with black, gray, or black magnetic powder. The print must then be photographed as outlined above, then the print can be lifted with wide, clear lifting tape or a large gelatin lifter. If tape is used, the tape must then be carefully placed on a piece of large, clear acetate, avoiding air bubbles as much as possible. The lift should be properly labeled, secured, and sent to the lab.
Whenever possible, chemical enhancement techniques for shoeprints should be done in the crime lab. At the lab, the proper facilities and trained personnel can safely handle some of the potentially hazardous chemicals that may be necessary for enhancing shoeprint evidence. When the shoeprint is located on a large, non-transportable item and the print cannot be cut out and sent to the lab, then the print may have to be chemically enhanced at the crime scene. In this case, someone from the lab who is knowledgeable in the various techniques should go to the scene and process the shoeprints. The scientist is more likely to have access to the safety equipment that should be used for a particular enhancing technique. If the crime scene investigator must enhance the print, then he or she must have the proper safety equipment, such as gloves, shoe protection, face protection, clothing protection, and/or respiratory protection. Some of the chemicals may be potentially corrosive or flammable, so the investigator must use extreme caution when utilizing these techniques. Crime scene investigators must also thoroughly read the Material Safety Data Sheets (MSDS) on every chemical used in the enhancing compounds.
Bloody shoeprints can be very important evidence in a crime scene investigation. The perpetrator’s shoeprints may be made with the victim’s blood. In many cases, the bloody shoeprints will be very obvious and require no enhancement; however, these obviously bloody shoeprints will usually only yield class characteristics to a shoeprint examiner. Since the blood heavily saturates the shoe, most, if not all, of the individualizing characteristics will be obscured. While these prints should be documented for their class characteristics, the crime scene investigator must concentrate on enhancing, the barely visible or latent bloody shoeprints. These prints are usually a few steps beyond the obviously bloody prints. As the perpetrator steps away from the main pool of blood, most of the blood will be deposited on the floor with each progressive step, so that several steps later a very thin film of blood adheres to the shoes. This film will transfer to the floor and leave an excellent quality latent, bloody print. The crime scene investigator must locate and enhance these prints. The investigator should also collect a representative sampling of the bloodstains present. If the prints are obviously from a pool of the victim’s blood, then this should also be documented.
Several blood enhancing reagents, such as ortho-tolidine, amido black, and merbromin, are available for use by crime scene investigators. Much has been written about luminol as a blood enhancing reagent; however, because it is water based and it doesn’t use a fixative, it could cause the print to run or smear if over saturated. An organic based reagent such as ortho-tolidine or merbromin evaporates rapidly so the print will not smear. Amido black is a water based protein stain that uses a fixative before treating the print so the print will not smear. Before using any of these reagents, some experiments should be done on bloody test prints placed on a variety of substrates to learn which treatments work better on which types of surfaces. The method of choice depends on the crime scene investigator, his or her experience, the surface substrate, and the techniques preferred by the investigator. The investigator must also remember that these enhancement reagents are not specific tests for blood. These reagents may also react with other substances, such as certain metallic ions and plant products.
Shoeprints may be made by substances other than blood. 8-Hydroxyquinoline will fluoresce under ultraviolet light when it reacts with calcium, magnesium, iron, aluminum, and other metallic ions. If the these substances are present in the print or the substrate, then 8-hydroxyquinoline can be used to enhance the print. If these substances are present on both the substrate surface and the print, then either minimal or no enhancement will take place. In an acidic solution, thiocyanate ions will react with iron to produce a reddish brown compound. This property makes it effective in enhancing wet residue and muddy shoeprints that are made from iron containing soil. This only works well on surfaces that will provide contrast with the reddish brown color. Other methods of enhancing prints are available, such as photographing bloody shoeprints on dark clothing with infrared film or using other blood enhancing techniques. Each crime scene investigator should work with his or her shoeprint examiner on experiments using different enhancement methods on various substrates with shoeprints made from different substances to find the technique that best suit the investigator and the shoeprint examiner. Communication between the crime scene investigators and the forensic scientists is of prime importance in maximizing the amount of information to be gained from crime scene evidence.
In cases without suspects, a limited amount of investigative information can be generated from shoeprints. If enough of the shoeprint’s class characteristics are present and the examiner cannot tell what brand of shoe it is, then he or she may submit a photo of the shoeprint to a shoeprint database. In the United States, the FBI maintains a shoeprint database to determine the manufacturer of shoes. In Europe, some countries, such as Finland and the Netherlands, have a more extensive database consisting not only of commercially available shoes, but also of crime suspects’ shoes.
If the database is able to provide a manufacturer of the shoe or if the examiner can determine the manufacturer from the print, then the examiner can contact the manufacturer in an attempt to generate investigative information. Some shoe manufacturers, especially the larger ones like Nike and Reebok, have people who assist law enforcement agencies and can provide them with available information on a type or model of shoe, such as how many of a certain size were manufactured and where they were distributed. The police may then be able to narrow down a field of suspects to a particular group based on the make, model, size, and distribution information of the shoe that made the shoeprint. This could be the best information generated from a shoeprint in a non-suspect case.
In cases with a suspect or suspects, the law enforcement agency should submit reference shoes from the suspect to the lab. Any or all pairs of shoes from anyone involved in the crime, such as victims and suspects, should be submitted to the lab for examination. Shoes or photos of shoe soles from anyone who worked the scene should also be sent to the lab. The shoeprint examiner may first eliminate the reference shoes from the law enforcement agents, emergency medical personnel, etc. who were at the scene. This is usually based on a comparison of the class characteristics of the reference shoes and the crime scene shoeprints. If they cannot be eliminated based on the class characteristics, then a study of the individual characteristics may be necessary to eliminate the shoes as a source of the crime scene prints.
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