Footwear impression evidence examinations have been carried out and applied for forensic purposes for over 200 years. According to literature, footwear identification dates back to 1786 in Scotland. The first case was worked by a local police constable and according to the circumstances, it could be argued that anyone can observe footwear impression evidence, compare features, and make positive identifications. From this viewpoint, footwear impression examination would become a “supplemental” task to all other forensic duties performed by forensic examiners. This perspective would imply that this science is not respected as a specialized science. But is it?
There have been major discussions and concerns with footwear examiners from around the world on whether there should be an established number of characteristics in order to provide a positive identification. This study focuses on and concentrates on the possible future insight of footwear examination and the understanding of the four basic components of a successful examination: the anatomy of the human foot, the outsole making process, the comparison/decision process and the presentation of the final conclusion within a courtroom.
Ernest Hamm of the Florida Department of Law Enforcement has stated that forensic footwear impression evidence is the oldest forensic science used in the world (Hamm, 1994). The oldest recorded forensic footwear identification dates from the Richardson case in Scotland in the autumn of 1786. During this case involving the murder of a young girl, the investigating officer located footwear impressions in a marsh near the cottage where the girl had lived. The trail of impressions was followed, and a few drops of blood and a bloody handprint on a step were discovered. The footwear impressions were described as boot prints and were observed to indicate a man in a running gait due to their deep impressions in the mud. Upon examination of the impressions the investigating officer noticed that the boot prints appeared to have new patches and a lot of nails in the outsole. The officer made a crude, but effective, plaster cast of the impressions. He would later compare the casts against the boots of individuals who appeared at the funeral of the victim, and it was through this process that he discovered the identity of the murder.
For over 200 years forensic examiners have been comparing unknown footwear impressions to known shoes of individuals. In performing these comparisons, examiners have utilized a variety of methods and techniques to arrive at a single conclusion. In a complete and unbiased examination the examiner must integrate together four basic strengths of that examination, 1) understanding of the anatomy of the human foot, 2) understanding the construction of the shoe itself, 3) understanding the comparison and decision making process, and, 4) understanding the proper and effective method in presenting the findings in a court of law. Each function has its place within the analysis and decision making process, but together they assist in arriving at the final conclusion.
Part I The Anatomy of the Human Foot
The process of footwear evidence analysis begins long before the examiner considers the item of footwear. The examiner must have a good working knowledge of the foot that wears the shoe and makes the prints. This includes knowledge of the bones of the feet and an understanding of how each bone functions in making a footwear impression.
The uniqueness of the human foot may be described as:
- Morphological: the visible form and structure of the foot;
- Biomechanical: the function of the foot; and
- The papillary ridge formations: the components that can provide positive identification based on the formation and unit relationship of the ridges.
The structural and functional components of the foot are composed of highly refined interrelated segments which provide a stable base for supporting the body when standing, running, walking and jumping.
Not all bones of the foot are present when when first born, nor even in childhood. The final primary and secondary bony structures will have gradually emerged by puberty. The human body contains 206 bones, approximately 1/10th of which are confined to the foot. The largest bones, the tibia and fibula, are in the legs. Each foot is comprised of 26 bones, 32 joints, and 112 ligaments plus two sesamoid bones, small bean-size bones partially encased in a tendon under the heads of the first metatarsal bones, which are perfectly designed. Seven thick, short, tarsal bones compose the heel and back of the instep; five parallel metatarsal bones, forming the front of the instep, spread toward the front of the foot to form the ball. Fourteen smaller bones make up the toes; the large toe is composed of two phalanges and each smaller toe has three phalanges. All the bones are firmly connected by tough bands of tissues called ligaments; the plantar ligament runs from the heel bone to the metatarsal, keeping the bones in place.
Our foot structure is arranged in order to support the body, maintain the stability of the body, and propel the body during its movement. One part of the foot supports the body while the other functions to propel it. In jumping off a countertop on to the floor; the foot propells the body off the countertop and also supports the force as the body contacts the ground.
The foot is divided into three segments: 1) rear foot or hind foot, composed of the talus (ankle bone) and calcaneus’s (heel bone); 2) midfoot, which is the navicular, cuboids, and cuneiform; and 3) forefoot, which is the metatarsal and phalanges. (DiMaggio, Dr. 1994) The tarsal and metatarsal bones form the two arches of the foot. The plantar arch runs from the heel to the ball of the foot and normally only touches the ground at each end. The metatarsal arch runs across the ball of each foot. These flexible arches, along with the thick layers of fatty tissue, absorb the pressure and the shock of walking and jumping, but because the foot cannot maintain the constant pounding of the human body, footwear-manufacturing companies have added extra support in the construction of shoes to assist in absorbing the pressure.
There are three basic foot types that affect the biomechanical needs of the feet. The normal foot has a normal sized arch and leaves an imprint that has a flare but shows the forefoot and heel connected by a wide band. The normal foot lands on the outside of the heel, then rolls inward (pronates) slightly to absorb shock. The flat foot has a low arch and leaves a nearly complete imprint. That is, the imprint looks like the whole sole of the foot. This imprint usually indicates an overpronated foot that strikes on the outside of the heel and rolls inward (pronates) excessively. The high-arched foot leaves an imprint showing a very narrow band connecting the forefoot and heel. A curved, high arched foot is generally termed a supinated or underpronated foot.
During the comparison of known shoes to unknown impressions, wearing characteristics that are observed can play an important part in an examination conclusion. Once the wear pattern begins it is hard to stop. That original pattern may not be unique, but as the wearing continues it will become unique to that individual. Since the foot can move in four different directions, this can influence the main portion of wearing characteristics on the outsole of a shoe: 1) plantar flexion, which it extends by pointing the toes downwards; 2) dorsiflexion, which it extends by pointing the toes upwards; 3) inversion, which it does during supination or inward motion; and 4) eversion, which it does during pronation or outward motion.
The human foot has its own uniqueness and in some cases, under specific circumstances, can be placed back to a particular shoe. It is important to remember that how a person walks and steps is not only controlled by the feet, but by the rest of the human body. Each part of the body contributes significantly to the activities of the feet and their process.
Let’s look at a few common foot ailments and see how they can affect the wear pattern of the outsole and possibly the inner sole.
Bunions: A bony growth on the side of the base of the big toe. Pressure from the shoe and motion at that joint can cause pain. The bunion is an arthritic condition that can result from a genetic defect and can cause biomechanical problems such as overpronation or tight fitting shoes.
Calcaneal Bumps: A bony protuberance behind the heel. They are most often associated with a high arched foot; the bony prominence pushes into the back heel counter of the shoe. With high arched feet, the heel bone (calcaneus’s) can change alignment, and this may cause an enlargement of the bone at the back of the heel. Sometimes the body will create a bursa, which is a sac of fluid that protects the tendon and other soft tissues. When wearing shoes, this bursa gets pushed up against the heel counter and becomes painful.
Hammertoes: The toe is usually bent or contracted. This condition usually occurs in the second, third, or fourth toes; also the little toe may be curved. Hammertoes result from a misalignment of the foot, and therefore the toes rub against the shoe. The condition may be inherited, but usually excessive overpronation causes the tendons of the toe to pull at an abnormal angle. Gradually, the toe will become bent, and eventually a corn will develop to protect the toe joint where it rubs against the shoe.
Sesamoiditis: Found beneath the ball of the foot, under the joint that moves the big toe, are two little bones called sesamoid bones. These bones can become bruised and inflamed, which will make the foot feel as if it were walking on a rock. Sesamoiditis usually occurs in runners with high arched, rigid feet. which don’t pronate enough. This combination causes a lack of pronation which in turn leads to an insufficient amount of shock to be absorbed. Also, if a bunion is present, there is a high chance of the development of sesamoiditis, as the bunion deformity can lead to more pressure on one of the sesamoid bones.
Each of the above mention medical problems can cause defects within the inner portion of the shoe, making it possible to establish the suspect as the dominant wearer of that shoe. In some cases these problems can also cause unique wear patterns on the outsole of the shoes. Naturally, wear patterns in a particular pair of shoes become more pronounced with increased activity in those shoes. For example, the feet of runners hit the ground an average of 1,500 times every mile. With each stride taken, the foot absorbs a force several times the weight of their body. They land, roll forward and push off, again and again and again. Each time this happens the conditions discussed above cause wearing, whether on the outsole or the inner sole. The question is whether this wearing is unique from person to person.
With regard to the idea that wear patterns have no relationship to underlying states, this is a highly unlikely conclusion. Studies using various forms of force plate technology have shown that characteristic motion and pressure patterns arise during gait cycles relating to specific states. If characteristic force and pressure pathways exist it must necessarily follow that any interface (the shoe sole) between the pressure source (the foot) and the ground must be affected in a similar way on each occasion that this interface is subjected to a characteristic pressure pattern. In short, extraneous variables must have an effect on shoe wear patterns.
Shoes as a whole can be manufactured from different materials which can wear at different rates. It is also conceivable that if the material is hard enough, foot function may be corrupted. Even more generally, the over-all shoe design can affect foot function such that wear patterns appear slightly different. For example, a well designed trainer that allows full foot function may allow a different characteristic representation of wear patterns than a shoe with ankle support, or a slip-on shoe. Similarly, if the shoe is too small, or too large, foot function and therefore wear patterns may also be affected. Different shoe manufacturing last types also exist, affording the possibility that shoes manufactured on different lasts may exert control over foot function in different ways, again affecting wear patterns. However, even with this multitude of variables it is important to remember that as shoes are worn in, the usual footstep will begin to produce a characteristic pattern for that foot/shoe relationship.
If all people are unique, then it’s logical to conclude that foot impressions left by that person are also unique. For over 100 years forensic scientists have accepted the theory (which is no longer a theory) that fingerprints are unique from individual to individual. Sir Francis Galton (circa 1880’s) stated that fingerprints would remain with an individual, never changing except in size, from before birth and until death. The ridge formations that make up an area of friction ridge skin will not be replicated in any other area of skin. They are unique in their unit relation and relationship order from one ridge to another. Now: let’s ask ourselves, is the human body unique? Are we unique from each other? Remember, to be unique, we must be in a single group or category by ourselves. If the human body, meaning each of us, is unique from the other, then so also is the foot impression left behind by an individual at a crime scene, and the foot impression on the insole of the shoe. Feet are controlled by the rest of the unique human body. Dr. Louise Robbins, an anthropologist, said, “No two individuals possess the same constellation of footprint traits. Ours is a growing science.” There may not have been volumes of experiments and data yet collected, but as with all forensic sciences we will not discontinue the ideas, concepts, and theories.
Part II Understanding the Basic Manufacturing Process
People have been wearing shoes for over 5,000 years, but shoe sizing systems are a fairly recent development. Many years ago, shoes were made or acquired in one of three ways: 1) custom-made by a shoemaker; 2) the individual made his own for himself or his family; and 3) buying second-hand shoes from a more prosperous individual (or receiving hand-me-downs within the family).
As seen with the discovery of a 5,000 year old Iceman, his shoes were self-made. Each shoe consisted of an oval piece of leather; the edges turned up and bound with strong leather straps. Microscopic examination illustrated that the material used, was in fact, leather and not fur. The soles were presumably made of cowhide. Attached to the straps was a net knotted from grass cords; this covered the instep and the heel. This device was intended to hold in place the grass stuffed into the shoes for warmth. The cord-net also covered the loop hanging down from the leggings. Attached to the sole leather were the uppers, presumably of fur, which then continued up the leg roughly in the form of a boot. This was tied around the ankle with grass cords.
The oldest shoe found in Western Europe before the Iceman was unearthed in 1874. It came from the Buiner bog in the Dutch province of Drente. On the basis of pollen analysis, this shoe was dated back to the end of the Neolithic period, or generally about 2500 BC. Unlike the shoes of the iceman, it’s sole and upper were made from a single, oval piece of leather. In later specimens, a seam in the front of an inverted T would be placed at the heel, ensuring a better fit. This would be tied around the foot with a leather strap, which passed through slits about 2 centimeters long (3/4 inch) placed some 3 millimeters (¼ inch) in front the edge. Even though there was nothing else remaining of this shoe, such as an inner lining, it was clearly constructed on a different principle from that of the Iceman’s footwear, which consisted of separate pieces of material sewn together.
The homemade process was relatively simple. The foot was placed on a slab of leather or other material and a sole was cut from it. A piece of leather or some type of cloth was laid over the top of the foot, cut to fit, then nailed or tacked to the sole. Nobody thought in terms of size or width; the shoes were basically made to protect the feet. It was simply a method of fitting the foot with a cover. Shoemakers would generally follow the same basic method except for much more skill and sophistication. The shoemaker would start with a foot tracing, sometimes making an impression of the foot in clay or plaster. He would measure the foot “mass” by using the hand-span methods; elsewhere with various spans of his hand he created a “last” (a form shaped like a foot). With this process, there was no sizing of shoes; just the taking of measurements. Each shoemaker measured in his own individual way, which he protected and guarded. These trade secrets, of course, precluded any possibility of a general shoe measuring or sizing system applicable to everyone. Once the last was made, the shoemaker kept it in his possession, assuring repeat business from the same customer. Also, the shoemaker would be able to continue making shoes of a finer quality than the homemade kind because of his shoemaking skills as well as individual artistry in styling.
Early shoes, more than likely, fit much better than today’s shoes, as they were custom made to each foot. But nevertheless, many points of modern fitting refinement were absent, such as tread design, collar fit, heel and arch fittings, vamp fit, etc.
How today’s athletic shoes are built.
Athletic shoes are divided into three basic components: the upper, the midsole, and the outsole. The upper portion of the shoe holds the foot securely over the midsole platform while providing flexibility and support. The upper may be constructed in leather, suede, or lightweight nylon mesh. The midsole is the cushion that cradles the foot and provides cushioning for stability. It can be made with lightweight foam, phylon, or polyurethane. The outsole is the bottom of the shoe that provides durable foot protection and traction on a surface. The outsole can be made with a solid durable rubber compound; a carbon rubber compound, a blown rubber compound, or a durable rubber hybrid that contains 10% recycled rubber.
Most people do not think about the type of athletic shoes they purchase or the type of sport they will be doing in the shoes. Podiatrists tell us that most people don’t even think about their feet, as long as the shoes look good. So why spend so much money and time on a pair of athletic shoes? Do shoes not all perform the same?
During life people will have walked from 150,000 to 200,000 miles. That’s about six to eight times around the globe! Throughout that journey, feet will be levers, balancers, and shock absorbers. Perhaps this is why Leonardo da Vinci called the human foot a “masterpiece of engineering…a work of art!” Each step of the way, we will bring our weight down directly on our heels.
Think about the body weight. Now multiply by the weight by three. That is the force that the heel will strike the ground with when running. Multiply the weight by eight. That’s what the ball of the foot will endure coming down from a basketball dunk. The majority of this force is transferred into the body immediately upon impact with the ground. This quick rate of impact is one of the main reasons so many runners suffer injuries.
Most of the larger manufacturing companies have done years of research, and construct shoes based on function within different sports. They provide protection from those impact forces wherever your foot needs it the most. The Nike-Air athletic shoe, for example contains within the shoe tough urethane membranes filled with pressurized gas. These Air-Sole units will compress upon impact, then immediately return to their original shape. This assists the foot in absorbing the full impact of the activity. In some cases the inner sole of the shoe will deteriorate faster than the outsole. This is because of the amount of force we apply to the inner sole.
Almost everyone in the United States has, at one time or another purchased athletic shoes of some type. These shoes can range anywhere from a few dollars to well over a hundred dollars, depending on the type and brand of shoe purchased. Most buyers don’t know or understand the reasons why many shoes are constructed, designed, and manufactured the way they are. Sadly enough, even experienced footwear examiners fail to maintain their experience and knowledge concerning the construction of shoes they examine.
As I sat down one evening in a shopping mall, waiting for my wife and kids, I watched a young lady try on numerous pairs of dress shoes with some difficulty. After she had purchased the shoes and proceeded to leave the store, I approached her and asked why she selected them. She responded, “They match my new dress.”
People will usually select their shoes for one of three reasons: comfort, appearance, or protection. Sometimes it’s humorous to watch people select their athletic shoes, because most people seem to purchase them for only one of the three reasons listed. Comfort or protection of the feet are usually disregarded; as long as the shoes look good, people are happy. It is not suggested that a separate pair of shoes be purchased for each sport, or our closets would look like a shoe store. A specific pair of athletic shoes can be purchased for more than one sport.
The athletic shoe is designed and constructed with four major concerns in mind: impact, repeated motion, lateral motion, and risk of ankle sprain. They are also designed with either unidirectional or multidirectional movement in mind. The unidirectional shoe should be used for straight-motion activities, such as running or walking, and the multidirectional shoe is for sports with lateral movement, such as basketball, tennis, or racquetball.
It is the biomechanical attributes and function of the foot upon which the construction of most athletic shoes is based. Manufacturing concerns include safety and comfort to the person wearing the shoe for a particular reason or event. This type of information can assist the buyer when purchasing athletic shoes and even the footwear examiner during the analysis of a particular case. In many cases, information related to the construction and reasons why shoes are constructed the way they are, can assist in the identification of the shoes that made the crime scene impressions.
The Outsole Making Process
Before the outsole of any shoe can be made, a design of the tread must first be developed and a template created. There are many processes to transfer a template to a mold, but the most common one is called the “hand milling” process. Hand milling uses what is called a pantograph to transfer a design from precut templates into a steel for aluminum alloy mold blank. There are other methods of designing outsole patterns such as CAD-CAM, where the design is generated and stored in a computer and the engraving arm of the pantograph then routs the design into a block of metal.
There are five basic methods of manufacturing athletic shoe outsoles, but these five methods fall generally into two groups: cutting and molding. Both cutting processes involve the trimming of the material itself affecting the final shape and size of the outsole. The three different types of molding processes are compression molding, injection molding, and open-pour molding. There are many variations and combinations of these five basic methods, but from a basic knowledge of these processes, the examiner becomes familiar with the foundation of outsole uniqueness.
Before outsoles can be cut, a process referred to as calendaring must be performed. This process involves passing a raw unvulcanized rubber compound through a series of three rollers under heat and pressure. The first two rollers form the material into a continuous sheet with the same thickness and the third roller contains the tread design to produce a textured outsole. Calandered outsoles often contain strips with words like, “Made in USA”, or “Made in China.” Many characteristics are formed during the calendaring process due to the material still being soft and open to flaws. These characteristics in themselves are usually not random characteristics, but can lead the examiner to a specific mold.
After the material has been calandered, the outsoles are cut in one of two fashions: a steel die or a knife blade. Usually, the steel die cuts the outsole as the calandered sheet is exiting the machine. The die cuts the outsole to the correct size and shape, much like cookie cutting. Some of these cuts are performed by machine while others are cut by hand, after the machining process. The second cutting method involves a machine called the Wellman outsole-cutting device. It utilizes a knife blade, guided by a template, to cut each outsole from the calendared outsole sheets. The calendared mold sheets can either be made or milled by the footwear manufacturers or they can purchase “premolded” sheets of material. The important thing to remember about cut outsoles is that the final size and shape of the outsole is determined by the cutting process. Molded outsoles take on the size and shape of the mold itself, which also contains the tread design.
Injection molding is a closed mold process where the outsole material is injected into a small port on the tightly-sealed mold. During this process air bubbles may occur, leaving unique characteristics on each outsole. Many of the injection molding processes have molds with two or three separate compartments and stations that enable the injection of one, two, or three colored outsole materials.
Compression molding involves the outsole material being placed on a molding device with hinges. The material is poured on one side while the other side is closed down on top, sandwiching the material in between. A considerable amount of heat and pressure is then applied, after which the completed outsole is removed and trimmed. The K-Swiss, Si-18 athletic shoe is a good example of a compression-molded outsole.
The open pour mold is where the mold of the outsole is open during the entire manufacturing process. Foreign material can fall into open molds causing imperfections within the outsole.
There are a variety of other manufacturing methods, and some manufacturers use a combination of the molding techniques already described. However, a general knowledge of the creation of the molds themselves offers even more insight to outsole uniqueness.
During the making of outsole molds, certain methods of construction lead to unique imperfections in the mold itself. Stippling is a process whereby a skilled designer will use small steel punches and a hammer to carefully hand-stamp a random design into the mold. The significance of stipled footwear is realized when an examiner, through a careful examination, is able to report more than just a correspondence in size and design, but is also able to determine that the impressions must have originated from outsoles from the same mold. In many examinations a footwear analyst along with the manufacturing company can provide pertinent information that may lead to reports that state:
“The unknown impression was made by a left shoe containing numerous characteristics from mold imperfections. It was determined that the unknown impression came from an outsole produced by the same mold as the known shoes. After contacting the manufacturing company, information was supplied that only 500 left shoes were made and sold worldwide that are consistent with the same mold imperfections that are visible in the unknown impression.”
Part III Understanding the Comparison Process
In today’s shoe market, there are a variety of different manufacturing companies which make thousands of different shoe designs, each of which comes in numerous sizes, shapes, and tread designs. Consequently, any particular shoe design in a particular size represents an item which is owned and worn by far less than one percent of the population. For example, take a room of one thousand people, and look at the shoes worn by each person in the room. You would see less than one percent of them with the same shoe (size, color, tread design, make, and model). Each time a new characteristic, such as color, wearing marks, or even random manufacturing characteristics is described, it reduces the number of people owning and wearing those shoes.
In addition to examining mold characteristics, there is also the possibility of detecting evidence that transfers from the crime scene to the shoe of the perpetrator. (Edmond Locard Exchange Theory, 1910) This type of evidence cannot only place a suspect at the crime scene but may occasionally show a certain degree of involvement in the crime. In certain situations where footwear impression evidence is collected properly and the known shoes of a suspect are obtained, comparisons can be made to determine positive identification.
A footwear examiner must learn to deal with each and every aspect of a particular shoe when making a comparison. The science of footwear examination rests upon the foundation that a questioned impression containing a sufficient quality and quantity of detail has the potential of becoming individualized with what is forcefully described as absolute certainty. There are three critical parts of a comparison examination that an examiner must take into account in order to perform a competent examination: the physical characteristics of the outsoles, the manufacturing techniques of the known shoe, and the wearing of the shoe by the foot. Each element can affect the final determination of the examiner.
Footwear examiners have always utilized outsole manufacturing characteristics and physical damage in the comparison process. It has not been until recently that examiners have begun to consider unique wear patterns from the human foot during the examination process. Before entering into a detailed discussion regarding the weight given to different types of detail during a comparison, it is important to establish the distinction between class characteristics, individual characteristics, and wear characteristics.
Class characteristics are the more obvious features distinguishable in an object. According to Bodziak, class characteristics are defined as “intentional or unavoidable characteristics that will be repeated during the manufacturing process and shared by more than one shoe.” Class characteristics can be divided into two areas for comparison purposes: general and limited.
As they apply to footwear, general characteristics are the basic design features in the outsole pattern. General characteristics are those outsole features that are totally indistinguishable between different outsoles. This type of characteristic is the weakest in the comparison and identification process, but they do serve as screening criteria for further comparative examinations.
Limited characteristics are those manufacturing or design features that can separate an object from another in its class. This is where the variation in mold design is distinguishable.
In many cases where only class characteristics are present, an examiner can positively state that the unknown impression was NOT made by a particular shoe. (elimination) These types of characteristics will include such features as specific shape, design, size or dimensions. Class characteristics are conclusive for purposes of elimination, but not for individualization. When all visible class characteristics are present and within tolerance for any distortions that may be present, the examination is extended and individual characteristics are sought in each of the known and unknown impressions.
Individual accidental characteristics have been defined as “the result when something is randomly added to or taken away from the original structure of the shoe that either causes or contributes to making that shoe unique.” These types of characteristics can appear on the outsole or the side of the shoe. Generally, accidental characteristics can be divided into two separate areas: damage and temporary characteristics. As described by Hamm (1995), damage accidental marks are those characteristics that are commonly associated with the random cuts, gouges, etc., made to the outsole during the wearing or before molding. Temporary accidental characteristics are the marks that result from foreign debris or substance becoming attached to the outsole. Matter such as gum, rocks, tape, or anything else that adheres to or becomes lodged in the contour of the outsole can transfer a unique pattern to the receiving surface resulting in a feature for comparison. Because of the transient nature of these types of characteristics, they can perhaps carry more weight towards a positive identification than most other types of marks because they can contribute towards establishing a critical time factor. It is through the comparison of individual characteristics that an impression can be individualized to one particular shoe.
As briefly discussed earlier, the understanding and knowledge of the anatomy of the foot and its function can assist the examiner in the utilization of wear characteristics in reaching a final conclusion. Wear characteristics are normally associated with accidental characteristics, but they really are not accidental. Wear is a change that results with time, actions of the wearer, and nature of the surfaces acting on the outsole. Wear can best be described as a continual changing of class characteristics, and certain accidental characteristics, resulting in individualistic features. Major concern in the field revolves around defining at what point a wear pattern becomes individual. The more extensive the wear, the more original the appearance when compared to another outsole of the same design.
There has been major worldwide discussion in the footwear examination community regarding whether there should be an established number of characteristics required to individualize an impression to a source. Robert Olsen, Sr. wrote, “There is no valid scientific basis for requiring a minimum number of characteristics which must be present in order to establish a positive identification.” The Search For Evidence, written by Art Buckwalter, states “that the impressions are unique only when the object that makes them has unique characteristics”. Webster’s II New Riverside Desk Dictionary defines “unique” as 1) being the only one, 2) being without an equal. Are footwear individualizations based on probability? If we believe in uniqueness of characteristics, then how can we possibly establish a specific number of those characteristics before we can state positive identification? Each characteristic is different, and must be weighed along with many other considerations during the comparison process.
In 1973 the International Association for Identification’s Standards Committee attempted to establish a minimum number of characteristics needed to prove positive a fingerprint comparison. The committee stated, ” … The International Association for Identification, assembled in the 50th Annual Conference at Jackson, Wyoming this first day of August, 1973, based upon a three year study by a standardization committee, hereby states that no valid basis exists at this time for requiring that a predetermined minimum number [of] friction ridge characteristics must be present in any two impressions in order to establish positive identification. The foregoing reference to friction characteristics applies equally to fingerprints, palm prints, toe prints and sole prints of the human body…”
Experience has demonstrated that in determining positive identification in footwear comparison, three types of criteria should be viewed without a standard minimum number of characteristics: the level of training and experience the examiner possesses; the quality or clarity of the known and unknown impressions, and the uniqueness or significance of the characteristics.
Any one footwear impression found at the crime scene may contain the specific feature that will be vital to the correct comparison of the unknown and known shoes. That special bit of information may not, and probably will not, be readily apparent at the crime scene. In most cases it is hardy ever apparent at the scene if a particular shoeprint or portion of the impression will later be critical in establishing a positive identification. Comparisons and individualizations usually occur long after the evidence is collected. Consequently, every impression, regardless of its condition and completeness, must be treated as though it were the only impression that has the potential of becoming a key piece of evidence in establishing a particular suspect location or action pertaining to the crime under investigation.
Test Impression Exemplars
Test impressions are a necessity to a good and competent footwear examination. Preparing good test impressions using the known shoes is a vital part of the comparison process. It has been observed over the years that many footwear examiners prefer to compare “like to like”, which simply means that if crime scene investigators submit a cast to the laboratory, the analyst will usually make a cast of the known shoes for the examination. There are good reasons why this preference exists. When an individual is wearing a shoe, minute cracks may expand and be represented as such in an impression. However, if photographs of the outsoles of the known shoes were to be used for comparison purposes, these small cracks would most likely not appear as prominent, and may not even be seen. This is why an examiner should always make appropriate test exemplars of the known shoes when making comparisons. Make those first impressions count!
Often, inexperienced investigators unknowingly limit the scope of examiner opinion simply because they don’t realize the importance of taking good known impressions. Poor or inappropriate test impressions can often limit an examiner to an opinion of “consistency”, whereas good quality “like” known exemplars would have resulted in individualization. Many cases have been worked in which the submitted test impressions did not show the characteristics needed, but once the “like” test impressions were made in the same manner as the unknown impressions, the characteristics reproduced.
Other simple mistakes can have a tremendous impact on whether or not a positive result is possible. For example, it is common for an inexperienced investigator to remove the suspect’s shoes, turns the outsoles upward, place a ruler over the outsole and take a photograph to be submitted for comparison purposes. It isn’t even realized that the random characteristic that might be needed for a positive identification could be located underneath the ruler that has been placed over the outsole of the shoe.
There are a variety of methods used in making test impressions for comparison purposes. Many examiners will adopt the habit of doing it the same way each time, but again it is emphasized that the same way won’t always be the right way. In order to obtain excellent contrast and to register the finest detail possible, test impressions should be taken using the best transferred material, which is coupled with the best receiving surface. In most cases, following a few simple rules and procedures insures a thorough examination, and therefore the best results possible:
- Review all the footwear evidence prior to any examination. Cast, photographs, evidence — by doing so, you save yourself valuable time by first learning what you have to work with.
- Process and examine all evidence that needs to be examined for possible footwear impression evidence. Photograph all footwear impressions.
- Photograph the known shoes prior to taking any test impressions, first showing the outsoles of both shoes and secondly showing the outsole of one and the side of the other. In doing this you now have a photographic record of the outsole as they appeared when you began your examination. Remember when recording test exemplars you may lift or remove debris from the outsole that could be used during the comparison process.
- Print all the crime scene photographs. Remember one photograph may contain detail that the others do not.
- Review the other evidence. Photograph any casts that were made. Casts are easily broken, especially if accidentally dropped. It is better to be safe now than sorry later.
- Make appropriate test impressions of the outsole of each shoe.
During some comparison processes the examiner may be able, based on tread design alone to eliminate the known shoes as having not made the unknown. This may prevent a lot of extra future work.
Part IV Courtroom Testimony
“The role of the expert witness is not to determine guilt or innocence, but rather to assist the court in determining what weight is to be placed on technical evidence entered which without assistance could not be interpreted properly.” — Cassidy, 1980.
The expert witness must be highly skilled and knowledgeable in their chosen area. They may acquire the requisite experience in a variety of different ways, ranging from on-the-job training to specialized training schools. For the most part, the expertise is gained from experience doing and using what has been learned, or by working under the direct supervision of an experienced and recognized expert. The title of “expert witness” is granted only by the court, allowing the examiner to give an opinion on any relevant issue that is within the scope of his/her expertise. The court will weigh the qualifications, experience, and demeanor of the witness carefully upon each court appearance. The balancing factor lies in the fact that the jury can decide the weight, or importance, of each expert’s testimony. If a juror feels the expert has not followed correct procedures, he/she may apply less weight and significance to the expert’s testimony, or even choose to ignore the testimony. Many very qualified footwear examiners exist who are considered “guns for hire.”
It is essential that the beginning expert be knowledgeable in all phases of footwear impression evidence. Keeping current on the latest developments and techniques within the crime scene field is an absolute must.
Our perception is our reality — the way we dress and present ourselves, as expert witnesses will create that initial impression to the jury during testimony. John F. Molloy once wrote, “that one’s dress and appearance convey strong impressions about the person’s ability, dignity, and even their character”. He also states that an individual’s dress can significantly influence personal and professional evaluation by others. In other words, first impressions are lasting impressions. It might be beneficial for an expert witness to consider themselves a salesperson that is selling his or her opinion to the judge and jury. Appearance is a major factor in the sales process, and can mean the difference between a sale and no sale.
Historically, the most appropriate attire for men in the courtroom has been a dark-colored suit that is comfortable and professional. Women have traditionally worn a skirted suit of knee length, also in dark colors. This traditional wear is changing due to the evolution of clothing over the years. The expert witness should avoid flamboyant jewelry that may detract from their testimony. If police personnel are required to wear their uniforms to court based on departmental policies, it must be emphasized that weapons, keys, handcuffs, and other police equipment should not be worn to the witness stand. Pagers and mobile phones should be turned off or left outside the courtroom. Nothing should be taken to the witness stand that may distract the jury and judge — or detract from the witness’s testimony.
Preparation for testimony should begin well before the examination. Develop an expertise with a commitment to practical experience, education, and keeping up on current developments in the science. Expand your knowledge of the basics: the anatomy of the human foot, the footwear manufacturing process, and the comparison process — and status as an expert in the field, and success in the courtroom, will follow. Never allow oneself to become caught up in testifying to an examination or the comparison of footwear impression evidence unless one has been properly trained and possess the experience, qualifications, and training of a footwear examiner. New cases may come along — but professional reputation may never be exchanged.
Footwear impressions evidence probably stands a better chance of being present at the crime scene than latent print evidence. It only needs to be, searched for, recognized, collected and preserved in a proper and effective manner to be of value. In many instances, the reason this type of evidence falls hopelessly short is due to a lack of training and education.
Ernest Hamm said it best, “It is time that the oldest form of applied criminalistics assumes its own identity and purpose”. (Hamm, 1994) This science is not a “supplemental” task to all other forensic duties; it is a discipline that requires years of experience, a vast variety of knowledge and training. It is the oldest form of criminalistics and we need to give it its own identity instead of giving it the title of an “additional duty.”
Dwane S. Hilderbrand, CLPE
Scottsdale Police Crime Laboratory
9065 E. Via Linda
Scottsdale, Arizona 85258
(602) 391-5278 Office (602) 391-5092 Fax
Note from the author: I would like to personally offer my sincere appreciation and thanks to those individuals that continue to fight the battles to build this fascinating and most exciting science to its fullest extent.
Some of the listed books are old and out of print, but they contained important information for the Author. Other articles of reference were used to prepare this paper with no documentation pertaining to author, dates or copyright were present to give credit.
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Abbott, John, FOOTWEAR EVIDENCE, Charles Thomas Publishing Company, 1964
Barrett, R., THAT’S SHOE BUSINESS, YOU DON’T NEED A DIFFERENT PAIR FOR EACH ACTIVITY, article written for The Arizona Republic-Life Section, March 27, 1995.
Bodziak, William J., FOOTWEAR IMPRESSION EVIDENCE, Elsevier Series, 1990
Bodziak, William J., US Department of Justice; FBI, SHOE AND TIRE IMPRESSION EVIDENCE, September 1986
Bodziak, William J., MANUFACTURING PROCESS, Presentation at the 78th International Association for Identification, Florida, 1993.
Buckwalter, Art, THE SEARCH FOR EVIDENCE, Stoneham, Ma., Butterworth Publishers, 1984, page 147.
Cassidy, Michael J., FOOTWEAR IDENTIFICATION, Canadian Government Printing Centre, 1980
David, RJ. Dr., CURRENT PERSPECTIVES IN FOOTWEAR IDENTIFICATION, Identification News, October 1986.
Dimaggio, John Dr., THE FOOT AND SHOE: AN IMPORTANT BUT OVERLOOKED IDENTIFICATION COMBINATION, International Association for Identification Annual Conference, Phoenix 1994.
Hamm, Ernest D., TRACK IDENTIFICATION, AN HISTORICAL OVERVIEW, International Symposium of the Forensic Aspects of Footwear and Tire Impression Evidence, FBI Academy, 1994.
Hamm, Ernest D., CHARACTERISTICS IN FOOTWEAR EXAMINATIONS, article written and presented for the 1995 European Meeting for Shoeprint and Tool Mark Examiners, Vantaa, Finland.
Hilderbrand, Dwane S., Paper entitled “ATHLETIC SHOES, WHICH ONES TO BUY AND WHY?”, Arizona Identification Council Newsletter, 1993.
Hilderbrand, Dwane S., FOOTWEAR, THE MISSED EVIDENCE, Paper presented at the International Association for Identification Annual Training Conference, Orlando, Fla, 1993.
Jaroff, Leon, READER’S DIGEST, Mystery of the Iceman, Condensed from Time, April 1993.
Kirk, Paul, CRIME INVESTIGATION, Interscience Publishers, Inc., NY 1953
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Spindler, Konrad, THE MAN IN THE ICE, Chapter on The Shoes, Phoenix Publishing Company, 1993.
Svensson, Arne; Wendel, Otto; and Fisher, Barry A.J., TECHNIQUES OF CRIME SCENE INVESTIGATION, Elsevier NY, 1981
Tang, Les; Regional Representative for Reebok International Corporation, Fall 1992 catalog.
Vernon, Wesley; Parry Anne; Potter, Mike; A paper written on MOVING TOWARDS CONSENSUS: THE FIRST DRAFT OF AN EVALUATIVE INSTRUMENTAL GRID TO INTERPRET SHOE WEAR MARKS, presented at the International Assoication for Identification 1996 annual conference.
Wilson, Colin, WRITTEN IN BLOOD: DETECTIVES & DETECTION, Warner Books, 1989, pages 46-48.