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.
Introduction
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:
1. Morphological: the visible form and
structure of the foot;
2. Biomechanical: the function of the
foot; and
3. 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:
1. 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.
2. Process and examine all evidence that needs to
be examined for possible footwear impression evidence. Photograph
all footwear impressions.
3. 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.
4. Print all the crime scene photographs.
Remember one photograph may contain detail that the others do not.
5. 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.
6. 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.
Conclusion
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
dhilderbra@aol.com
