Once upon a time there was a prince who hosted a huge party at the royal castle. At the gala, one female stood out from the others at the dance, her name was Cinderella. Cinderella was able to attend the party because of a magical godmother who was able to turn a pumpkin into a coach, mice into horses, her old clothes into a beautiful ball gown, and gave her glass slippers (Perrault, 1697). Cinderella was told that she had to leave the party by midnight because everything that her magical godmother had transformed would turn back to their normal state. As the night continued on and eventually approached midnight the beautiful Cinderella had to leave the prince’s company in a hurry. During her exit, Cinderella left behind a glass slipper (Perrault, 1697). The prince was so intrigued with Cinderella that he went out into the village with the glass slipper to see if it fit the woman he had met at the gala the night before. The prince tried the shoe on several women’s feet, but it did not fit. Eventually, the prince placed the glass slipper on Cinderella’s foot, and it was a perfect fit. The prince was so happy that he had found Cinderella that he married her, and they lived happily ever after (Perrault, 1697). While this old fable is well known, it demonstrates the uniqueness of our feet and how forensic podiatry works. Forensic podiatry can either link the shoe to the suspect or prove it doesn’t belong to a person in question (Earnshaw, 2008). A human footprint can tell a forensic specialist more than a fingerprint. Footprints can be examined and an approximation of someone’s height and how a person walks can be obtained (Earnshaw, 2008). Forensic specialists can examine a person’s footwear and also determine if the suspect in question has any foot deformities or other structural medical conditions, such as bad knees (Earnshaw, 2008). Another benefit of examining footprints at a crime scene is the higher possibility of obtaining a successful footprint or shoeprint. For example, a criminal can wear gloves and hide his fingerprints at a crime scene but it is extremely rare if a criminal can enter a crime scene without using their feet (Earnshaw, 2008).
Even without scientific proof, people have long considered footprints to be different and unique. The presenting of footprint evidence in court dates back to the late 19th century, when a criminal named LeDru was convicted in 1888 based on footprint evidence (Kennedy & Yamashita, 2007). One of the earliest documented footprint evidence cases in North America occurred in Canada in 1948 (Kennedy & Yamashita, 2007). The Kett brothers were accused of a series of burglaries. One of the brothers, William Kett, stated that he was innocent and that a pair of shoes matched to the crime scene belonged to his brother Donald, who had already been convicted. The pair of shoes that were recovered at the crime scene were cut open and the impressions were compared to Williams’ feet, which matched and lead to his conviction (Kennedy & Yamashita, 2007). Many of the earlier court cases relied on the assumption that barefoot impressions were unique to an individual, although no research had been done to establish this. Recent research has backed up the theory that barefoot impressions are unique to an individual. Since, like fingerprints, not every footprint in the world can be collected and compared; extensive studies have been done on barefoot impressions. These studies have concluded that the probability of a random match to an impression is 1 in 1.27 billion, indicating the variability of barefoot impressions (Kennedy & Yamashita, 2007). A current footprint database, called AutoCAD, has also determined and confirmed the individuality of footprints.
The uniqueness of the human foot can be viewed as morphological, biomechanical, or with the papillary ridge formations on the foot. Morphological characteristics are the visible form and structure of the foot (Hilderbrand, 1999). The human foot structure is arranged in a way of order to support the body. One part of the foot functions by supporting the body while other parts function to propel it. Foot morphology can best be described as how the foot moves and its affects the way a shoe fits during movement. Morphological characteristics allow forensic examiners to establish a link between the barefoot of a suspect to an impression left at a crime scene.
Biochemical characteristics relate to the functions of the foot. These would include foot ailments or medical conditions that effect the way a person walks and the uniqueness of wear on an individual’s shoes. Foot ailments such as bunions, calcaneal bumps, hammertoes, and sesamoiditis can have an effect on the inside of the shoe. In addition to foot defects, injury to the back, hip, knee, or leg can cause the individual to walk differently and thus change the weight-bearing areas of the foot (Kennedy & Yamashita, 2007). In some of these instances, foot problems can also produce distinctive wear patterns on the outsole of individual shoes (Hilderbrand, 1999). Wear patterns can be unique inside the shoe also due to other biochemical characteristics. With each step that is taken, heat is generated and sweat becomes present inside a shoe, causing it to stretch and conform to the shape of the foot (Kennedy & Yamashita, 2007).
Papillary ridge formations are the components that can provide a positive identification based on the formation and unit relationship of the ridges on the bottom of the foot (Hilderbrand, 1999). Papillary ridge formations are similar to the structure of fingerprints. The foot is also comprised of highly refined interrelated segments that provide a stable base for supporting the body when standing, running, walking, and jumping. With each movement of the body, the foot or shoe leaves behind a mark according to Locard’s theory.
Footwear evidence can be found in two forms, impressions and prints. An impression is an indentation that can be found in mud or other soft materials. A print is made on a solid surface by dust, powder, or a similar medium (Hilderbrand, 2007). Footwear evidence can be divided into three categories of crime scene prints, just like latent prints. These include visible prints, plastic prints, and latent prints. Visible prints are made when the suspect’s footwear steps into a foreign substance and is contaminated by it, then the footwear comes into contact with a clean surface and it is pressed into that surface. The print can be visibly seen by the naked eye without other aids (Hilderbrand, 2007). Plastic prints are impressions that occur when footwear steps into a soft surface, like snow, mud, wet sand, or dirt creating a three-dimensional impression. These types of impressions allow forensic examiners to see length, width, and depth. Latent prints are the most overlooked at crime scenes and are usually found on smooth surfaces.
When processing a crime scene, a slow visual search should be completed for the possible discovery of shoeprints after initial crime scene photographs have been taken. The crime scene should be protected so that footwear and barefoot evidence is not lost and destroyed. Forensic crime scene technicians should always, as on any crime scene, take every step to preserve the integrity of the crime scene from further contamination. Suspected areas where the suspect might have walked should be carefully visually examined for possible latent prints. The most efficient way to search for shoeprints is to darken the room and use an intense oblique lighting source on the areas were suspected shoeprints might be located. Often times, the less visible imprints are the ones that leave the finest details for comparison (Hilderbrand, 1999). If latent prints are still not visible under oblique lighting, the area can be searched with black gel lifters. The black gel lifters can aid in viewing latent prints in oblique lighting that was not previously seen (Hilderbrand, 1999). After locating any prints, proper crime scene photographs should be taken of the scene and documented. Most prints can be enhanced to provide further detail, but as stated earlier, before any enhancement is made, evidence quality photographs need to be taken. Taking photos prior to any attempt at enhancement will help retain the evidence in case enhancement techniques destroy the impression.
Shoeprints that are found in crime scenes should be treated as fragile evidence and can deteriorate over time. In some substances, time is of critical importance in the successful recovery of shoeprints. The six most common reagents that are used at crime scenes where aged shoeprints are found are Ninhydrin and Diazofluorenone of the amino acid staining techniques, amino black and coomassie blue of the two protein staining techniques, and leucocrystal violet and fluorescein of the two peroxidise staining techniques (Morgan-Smith, Elliot, & Adam, 2009).
A study conducted by Morgan-Smith, Elliot, and Adam (2009) compared common floor coverings and shoe patterns in different elapsed time periods to determine how long shoeprints would last and which methods were best for collection and enhancement of the prints. Morgan-Smith, Elliot, and Adam (2009) conducted the tests on surface areas of carpet, linoleum, varnished wood, and paper. They discovered some interesting findings on time lapses and the processing of shoeprints. Indoor impressions were shown to deteriorate the least, followed by outdoor sheltered areas, and then areas of open exposure. Footwear impressions on paper showed the least deterioration and the impression on linoleum showed the most (Morgan-Smith, Elliot, & Adam, 2009). For untreated footwear impressions on paper in a sheltered outdoor area, many previously visible features were lost within three weeks. The outdoor impressions on linoleum flooring appeared to be washed away after one week of exposure to periodic rain (Morgan-Smith, Elliot, & Adam, 2009). As far as enhancement of aged shoeprints, it was determined that amino acid provide the best enhancement on wood flooring and linoleum after 16 weeks of exposure (Morgan-Smith, Elliot, & Adam, 2009). While this experiment did not scientifically show a specific life span of visible shoeprints, it showed that even weeks after a homicide scene had occurred valuable shoeprints could still be recovered at a scene.
If a footwear or barefoot print is located in blood, then a blood reagent may be used according to the medium of the surface area (Kennedy & Yamashita, 2007). Fingerprint powder can be used on concrete, wood or vinyl floors, or countertops in crime scenes where no blood is involved. In prints that appear dusty, potassium thiocyanate can be used since it reacts to iron that might be present in the soil (Kennedy & Yamashita, 2007). If salt is used during the winter months, then a silver nitrate solution can be used to process possible prints.
After a print has been enhanced or made more visible, it should be photographed again with a scale and lifted. If the print is located on a surface that can be cut, the area around the print can be cut out and kept as an exhibit (Kennedy & Yamashita, 2007). Prints that are in dust or are dusty can be lifted with an electrostatic dust lifter. An electrostatic dust lifter generates a static charge that is applied to a sheet of foil that is placed over the print. The dust is attracted to the foil sheet by static electricity, allowing the print to be properly lifted for processing (Kennedy & Yamashita, 2007). If a print is found on a piece of paper on the floor, it should be photographed and the electrostatic dust lifter should be used prior to moving the paper. After processing the paper, the paper should be taken back to a lab for further processing (Kennedy & Yamashita, 2007). As with any type of evidence, every movement should be properly documented when moved and a proper chain of custody must occur.
Footwear or barefoot impressions are processed completely differently than prints found at a crime scene. Initially, the crime scene is photographed along with the foot impressions. These impressions, or plastic prints, are three dimensional and are commonly made in snow, mud, wet sand, or dirt. The impression is basically a negative cast of the shoe or foot. Unlike visible prints or latent prints, plastic prints usually do not generally show the same amount of detail as two dimensional prints (Hilderbrand, 2007). Once the plastic print is photographed with scales and other crime scene photos, a cast should be completed. The most common choice for preservation of a plastic print is dental stone. Dental stone is a form of gypsum that is hard enough to clean without the loss of detail. Dental stone is also much stronger than other casting methods and does not require that reinforcement material be placed in the cast during the pouring (Wolfe, 2008). Before casting the impression, it is important to make a form around the plastic print. This form can be made out of heavy cardboard or wood. The form should not be placed too close to the impression, because doing so might risk distorting the impression. After the form is made, the casting material should be mixed. In order to make a cast, the casting material usually comes in a zip lock bag which can be used to mix with water. Typically, 6 to 9 ounces of water per pound of dental stone is added into the zip lock bag (Hilderbrand, 2007). With the water inside the bag, the contents are mixed for about 5-7 minutes until they are a pancake batter consistency (Hilderbrand, 2007). Before pouring any mixture into the impression, talcum powder can be sprinkled over the impression which gives it a fixative. When using talcum powder, make sure not to over sprinkle, because doing so will lose details. Pour the mixture onto a spoon or a stirring stick while holding the spoon or stick to the side of the impression. The dental stone mixture should never be poured directly into the impression, because this will lose some if not all detail. Once the cast is poured, it must set undisturbed for at least 30 minutes, after which it can be lifted. When lifting the impression, use a knife or the spoon to pry the cast upwards. The cast should easily break free from the surface. Some soil or dirt made adhere to the cast, but do not remove it. The cast should then be air dried for 24-48 hours before cleaning. The cast should never be placed in a plastic bag for drying, since it will not dry appropriately. Once the cast is dried it can be carefully cleaned with a potassium sulfate solution with virtually no loss or erosion of detail from the surface (Hilderbrand, 2007). For different surfaces, the techniques for lifting a successful impression are varied.
Often times in colder climates, the impression might be located in snow. This type of impression should be processed just like other three dimensional impressions with proper photographing and documenting. A form should be placed around the impression and snow print wax can be sprayed over the impression and allowed to set for about 10 minutes. If snow print wax is not available, talcum powder or grey primer spray paint can be sprayed lightly over the impression (Wolfe, 2008). Just as mentioned above, you repeat the same process for pouring of the dental stone into the impression but allow the mixture to cast for 60 minutes with very cold water. Often times, technicians will place a box over the casting impression due to the long casting time to protect the cast (Hilderbrand, 2007). The cast can then be removed and should be dried for 48 hours.
In warmer wet climates, an impression might be in muddy water. Most people would assume that the impression is unliftable, but that is not the case. Just as with other types of impressions a form should be placed around the impression after it is photographed. The form should be large enough to come above the waterline. If there is any debris on the surface of the water, it should be removed very carefully. Instead of pouring the dental stone, it should be sprinkled in its powder form over the area of the impression very carefully (Hilderbrand, 2007). The sprinkled dental stone should be about one inch and allowed to settle. After the dental stone has settled, a mixture of the dental stone can be poured into the impression. This dental stone mixture should be thicker than normal and allowed to dry for 60 minutes. The cast should then be air dried for 48 hours after removal.
The benefits of casting an impression are numerous at any major crime scene. The cast gives lifelike and actual size molding of the original impression including uneven surfaces and depths that a photograph cannot show. The cast also gives reproduction of microscopic characteristics. In deep impressions, the cast impression gives reproductions of characteristics of the side of outsoles and midsoles of shoes which usually are not reproduced in photographs (Hilderbrand, 2007). While casting does not eliminate the need for photographs, it backs-up the photographs but also eliminates focus and scale problems.
The next step in the evaluation of footprint or footwear process is the collection of known impressions from individuals either for the elimination or inclusion process. Footwear worn by a suspect should be seized via search warrant and other shoes should be seized for comparison processes. All areas of the shoes should be photographed and the suspects’ feet should be photographed from every angle as well with a scale. These photographs will aid the examiner in determining placement of toes and foot flexes, and if any damage has been done to the foot by the footwear (Kennedy & Yamashita, 2007). Investigators should also attempt to obtain height, weight, and physical deformities that might affect the way a suspect stands or walks. Molded impressions should then be taken of the suspects’ foot using a foam material and other casting methods. The suspect should have his foot above the foam material, gradually increasing the weight on his foot into the foam until the bottom of the foot is half way through the box of foam (Kennedy & Yamashita, 2007). The foot should then be pulled out of the foam and a dental stone casting should be completed making a positive cast of the suspects’ foot.
Besides casting impressions of the suspects’ feet, inked impression and photographs should be taken also. These should be taken with the suspect standing and walking with and without socks, so that any discrepancies that might be present between the standing and walking impressions (Kennedy & Yamashita, 2007). During this process the bottoms of the feet are covered in fingerprint ink and the suspect is told to walk the length of a 5 to 6 meter long piece of white paper. It is extremely important that the suspects’ walking pattern be watched to make sure that they are walking normally. If socked impressions are being collected the suspect should wear a pair of thin socks and the bottoms of the suspects’ feet should be inked and the same process should be repeated (Kennedy & Yamashita, 2007).
When obtaining standing inked impressions, the suspect stands on an inked pad and then sits with his feet on the floor. A white sheet of paper is then placed in front of the suspect and then the suspect is told to stand on the piece of paper. A socked impression is obtained the same way, except for the suspect is asked to wear a thin pair of socks (Kennedy & Yamashita, 2007).
Once the suspect’s impressions are collected then an expert can compare those collected against impressions or prints obtained at a crime scene. The same process should be completed for eliminating prints of first responders, possible witnesses, or victims. The footwear/ footprint expert will first examine the class characteristics of the impressions. These include the outsole size, specific shapes of the foot and shoe, the dimensions, and specific design or logo. Because a class match is the lowest type of match to make, additional comparisons should be made. These additional comparisons should be individual characteristics such as a scratch, tear, air bubbles, or an inclusion of a foreign object into the sole of the shoe. Either a large combination of class characteristics or the existence of random individual characteristics should be used to match a suspect to a crime scene, set of shoes, or other collected footprint or footwear evidence. It should be noted that it is not possible to statistically determine the probability of specific damage to a piece of footwear. But if an expert can determine that the shoes damage could not occur on another sole, then a positive comparison can be made.
When examining the foot, it is usually more beneficial for a forensic podiatrist to examine the evidence to make a more conclusive comparison. The forensic podiatrist can analyze podiatry treatment records of the suspect, bare footprints, footwear, and forensic gait analysis. They can look at impressions and shoe wear to determine or rule out foot-related pathologies that are functional (for example, forefoot varus), structural (hammer toes condition), and superficial (sites of corns and callus) (Vernon & McCourt, 1999). Forensic podiatrists also examine friction ridge detail and other relevant skin features on barefoot prints, which can be used to make a link between a crime scene and a suspect. Occasionally, a forensic podiatrist will ask for assistance from a forensic anthropologist that is experienced in structural dimensions of the foot to the body frame to determine the body dimensions of a possible suspect. When examining footwear a forensic podiatrist can interpret functional pathologies of the foot and gait which may be manifested in outsole wear patterns of footwear and relate these functional pathologies of the foot and gait (Vernon & McCourt, 1999). Also, forensic podiatrists can also access wear features of footwear which relate to function and fit of the shoe to establish links between a known person and the questioned shoe, or between different sets of footwear items (Vernon & McCourt, 1999).
Footwear impressions and prints are just as important as other types of evidence collected at major crime scenes. Often the lack of training and education in the proper searching, collection, and preservation of footwear and footprint evidence is a cause of overlooking this type of valuable evidence. Also, footwear and footprint evidence is assumed to be undervalued or not understood by those responsible for collecting evidence and analyzing the crime scene (Hilderbrand, 2007). Failure to properly collect footwear and footprint evidence often occurs because of incomplete searches at the crime scene, weather conditions, or not believing that the impressions can be found at the scene after first responders have walked over the scene (Hilderbrand, 2007). First responders and forensic evidence experts should be aware of the high probability of obtaining a good quality footwear or footprint at any major crime scene. Footwear impressions and footprints stand a better chance of being present at a crime scene than latent prints. For example, a criminal can wear gloves and hide his fingerprints at a crime scene but it is almost impossible for a criminal to not walk into a crime scene and leave something behind. But in order for footwear and footprint evidence to be used it must be searched, recovered, collected, and preserved in a proper and effective manner to be of value. Unfortunately, this type of evidence is not usually collected due to lack of training and education supplied to crime scene investigators and first response officers. With additional research and more education this science has the potential to become a staple in crime scene investigations just as collecting fingerprints has. With new advancements in technologies, footwear and footprint impressions may lead to the proper convictions of potential burglars, rapists, and murderers.
References
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Morgan-Smith, R., Elliot, D., & Adam, H. (2009). “Enhancement of Aged Shoeprints in Blood”. Journal of Forensic Identification, Jan/Feb; 59 (1), 45-50.
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