Introduction

Introduction

 Hair is mainly composed of a protein called Keratin, which is the same protein that makes up your fingernails and the horn on a Rhinoceros! While hair may look very diverse, it actually has the same morphology, or structure, in all humans. The three main parts of the hair are the cuticle, the cortex, and the medulla. To visualize the structure of a hair, think of it as a pencil. The outer thin layer known as the cuticle, is similar to the paint on the pencil. The next layer, containing the pigments is the cortex, and it would be respresented as the wooden part of the pencil. Finally, the innermost layer, known as the medulla, can be thought of as the lead in the pencil. Hair evidence is tricky and can be both class and individual evidence. Part of the hair cycle that makes this evidence so tricky is that everyone routinely sheds hair which means that hair is everywhere. Even if a hair has nuclear DNA attached, it is often difficult to show that the hair actually belonged to the perpetrator of the crime and not someone who merely passed by the crime scene. Fibers and botanical remains are also often found at crime scenes, and just like hair evidence, can become cumbersome to analyze due to their abundance. Cotton is the most common fiber found, and is even a large componenet of household dust! Some cases have remarkable and unique fiber or botanical evidence, but this is not often the case. A Forensic Investigator certainly has to remember the limits of this type of trace evidence when investigating a crime scene!

Essential Questions

• What are the parts of a hair and how does it grow?
• How is hair evidence collected and analyzed?
• What are the different types of fibers typically found in a crime scene?
• How is fiber evidence collected and analyzed?
• What botanical remains are typically found in a crime scene and how are they analyzed?

Module Minute

Hair is an abundant type of trace evidence found at nearly all crime scenes. The abundance of hair in crime scenes, and the fact that everyone routinely sheds hair as part of the hair growth cycle, makes it very difficult to separate hair samples from the victim and their associates from those left by the perpetrator. Hair evidence based solely on morphology can't be used to identify an individual. In a morphological match, it can only be said that the hair sample from the crime scene is consistent with the suspect hair sample. To identify an individual from a hair sample, nuclear DNA must be obtained from the hair follicle. Fibers found at the crime scene often present challenges to investigators. Fibers can sometimes be linked to a suspect if the fiber is sufficiently unique and is found in the suspect's possession and at the crime scene.

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Identification and Comparison of Hair

Identification and Comparison of Hair

Many objects can connect a suspect to a victim or a crime scene; the key is to compare these items to trace evidence found in or on the suspect's person, home, car, or other belongings. Hair and fibers are examples of trace evidence that can be compared to make these connections. The processes involved in examining hair and fiber are very similar, yet each can yield unique and significant information. 

 The study of the scalp and hair is called trichology. Hair evidence can be transferred during the commission of a crime, so it can be used to establish an association of a suspect with a victim or a crime scene. Before proceeding, it is important to note that it is NOT possible to link hair to a specific individual based on morphology, or structural characteristics of the hair, alone. The value of hair is that it can provide corroborative evidence for placing an individual at a crime site. There has been increasing controversy over the use and interpretation of hair comparison evidence because on occasion, it has been misused. However, under specific conditions, hair may provide DNA evidence which is a valuable forensic resource. Another important contribution from hair evidence is that of toxic substances that may be present in the body. Hair can be tested for toxic substances such as illegal drugs or poisons even after they have been metabolized and excreted by the body. Some substances remain in the hair for months after the last use or exposure! Hair can thus be a very important part of Toxicology testing.

Morphology and Structure of Hair

Hair is made up of a protein known as Keratin; it is the same protein that fingernails are made of. Hair grows from the papilla which is a large structure at the base of the hair follicle. The papilla is made up mainly of connective tissue and a capillary loop. It is responsible for connecting the hair to the body's blood supply and nutrients via the capillary loop. Surrounding the base of the hairs are tiny muscles known as Arrector Pili muscles. These tiny muscle fibers are attached to each hair follicle, which contract to make the hairs stand on end, causing "goose bumps". Arrector Pili muscles are found in most mammals including humans. Another important structure involving hair is the Sebaceous Gland. The Sebaceous glands are small glands in the skin which secrete a lubricating oily matter (sebum) into the hair follicles to lubricate the skin and hair.

 The basic structure of hair is composed of three regions: the cuticle, cortex, and medulla. Each of these regions has unique structures that can assist investigators in identifying which species the hair came from as well as other characteristics. When thinking of the structure of hair, consider that a hair is like a pencil. A pencil has a thin outer covering of paint followed by a thicker middle layer of wood that surrounds a central layer of "lead" or graphite. A hair is structured in much the same way. Hair has a thin outer covering known as the cuticle, followed by a thicker middle layer known as the cortex and an innermost layer known as the medulla.

Cuticle

 The cuticle is the protective coating made of overlapping scales. The scales always point toward the tip of hair and produce a characteristic pattern that can be used for species identification. While there are some variations, there are three basic scale patterns: coronal, spinous, and imbricate.

 Coronal scales are described as a crown-like scale pattern found in hairs of very fine diameter which resemble a stack of paper cups. Coronal scales are commonly found in the hairs of small rodents and bats but rarely in human hairs.

Spinous scales are petal-like scales which are triangular in shape and protrude from the hair shaft. They are found at the proximal region of mink hairs and on the fur hairs of seals, cats, and some other animals. They are never found in human hairs.

Imbricate scales are flattened scales; consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs, and resemble puzzle pieces under magnification.

Preservation of the scale pattern can be accomplished by laying a piece of hair in a thin layer of clear nail polish on a slide, allowing it to nearly dry, and then removing the hair. The scale pattern can then be view by viewing the slide using a microscope.

Medulla

 The center of the hair, known as the medulla, is surrounded by the cortex. Not all hairs have a medulla, but when it is present in humans, it is one of three different types: fragmented, interrupted, or continuous. Animal hair can have special types of medulla patterns not found in humans such as Ladder, or Lattice. These distinct medulla patterns help to differentiate between human and animal hairs if there is question about the origin of the hair. It is important to note that Medullae are only found in animal hair (including humans), and are never found in plant fibers!

Scientists are still not sure of the purpose of the medulla, but some believe that it may be simply an air space within the central portion of the hair.

The presence of a medulla can vary, even from hair to hair in the same source. People of European and African descent may have fragmented medullae or they may not have any medullae at all. People of Asian descent usually have continuous medullae. Most other animals have continuous or interrupted medullae and the shape of the medulla can help identify different species.

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Collection of Hair Evidence

Collection of Hair Evidence

Recall that morphological characteristics are not considered individual evidence, and thus they can't be used to link a human hair to any single head or body. When a suspect is available, the collection of several hairs as standards/reference samples can provide strong circumstantial evidence, but not positive identification. Most often, scale structure, medullary index, and medullary shape are used for comparison. The value of hair evidence relates to the degree of probability associated with a questioned hair and a particular individual.

Body Area

The structure of hair differs on different parts of the body. There are several subtle characteristics that can help investigators determine which part of the body the hair originated. Hairs from the scalp have consistent diameters and uniform distribution of pigment. Pubic hairs typically have continuous medullae. Facial or beard hairs have triangular cross-sections and eyebrow hair decreases in diameter from the root to the tip. In addition, there are other various types of hairs found on the human body at various points in growth and development. Lanugo, a coat of delicate, downy hairs, is typically found on human fetuses prior to birth. Babies born prior to full term gestation may retain the lanugo hair after birth for a short period.

Another type of hair that is associated with growth and development is Vellus hair. Vellus hair is the fine hair present on the body after birth and before puberty. Once a person reaches adulthood, they typically have what is known as terminal hair.

Race

It is not always possible to determine race from hair samples. Some characteristics are common in each race, but there are always variations and exceptions.

People of Asian descent typically have continuous medullae. The pigment granules are generally very dense and occur in large patches or streaks. In cross-section, the hairs are almost always circular. Hair color is almost exclusively black.

People of European descent have an even distribution of pigments in cortex and may have fragmented or completely absent medullae. In cross-section, the hairs appear to be irregularly shaped ovals. Hair color varies from blonde to black; this group of people have the most variation in hair color.

People of African descent are more likely to have dense and unevenly distributed pigment granules. In cross section, the hair is often thin and appears somewhat flattened. The medulla is typically fragmented or absent. Hair color is generally black with some variances noted in individuals with albinism or European ancestry.

Identification & Comparison of Hair

It is usually very easy to compare animal hair to human hair, but comparing human hair to other human hair is difficult. Most commonly, forensic analysis is used to determine whether or not hair recovered from a crime scene is comparable to hair removed from a suspect. The analyst will look at morphological characteristics such as color, length, diameter, medulla, and scale pattern. If hair has been forcibly removed the follicular tag may be present which is a rich source of DNA which can then be used to identify an individual. A strand of hair with no follicular tag, or "root", would then be class evidence since it can't be linked to a specific individual. A hair with a follicular tag can be considered individual evidence if DNA can be extracted from the hair and analyzed to link it to a specific person.

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Types of Fibers

Types of Fibers

Locard's exchange principle states that materials are exchanged when two objects come in contact with each other. The exchange of fiber evidence can occur as the clothing of the victim and the suspect come in contact with each other as well as fibers at the crime scene. A textile is an artifact made by weaving, felting, knitting, or crocheting natural or synthetic fibers. Textiles can be initially categorized by their weave patterns. Further examination of the individual fibers would reveal the type of fiber, length, color, and method of spinning. Fibers can also be classified as natural or synthetic (man-made).

Natural Fibers

Natural fibers originate from plant and animal sources. They have been used throughout history in all climate regions to meet the needs of the people who lived there. Native plant and animal species were relied upon for fibers to create clothing, items for the home and even to manufacture tools! The most widespread plant fiber today is cotton. Because cotton is so common, its value as evidence is almost insignificant. Animals such as sheep, rabbits and goats account for some of the more common natural animals fibers. Wool is the most common animal fiber and is often used in the manufacturing of clothing and carpeting. Finding wool or cotton fibers at a crime scene would not be all that helpful unless the wool or cotton fibers had a distinctive characteristic or could be linked to a suspect in some way. Less common animal fibers such as Angora or Mohair could potentially be more helpful in an investigation simply because they are more rare. Finding a pale pink Mohair fiber is much more unusual than finding a gray wool fiber, for instance. Fiber evidence, as mentioned, is class evidence, so it requires careful analysis and corroborating evidence to be useful in a case. While fibers alone generally are not sufficient evidence for a judicial decision on a case, several types of class evidence can be compiled and a probability can be calculated which suggests a link to a specific suspect.

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Identification of Synthetic Fibers

Identification of Manufactured or Synthetic Fibers

Synthetic Fibers

Synthetic fibers, also known as Man-made fibers, can be made from either natural or synthetic polymers. A polymer is a substance composed of a large number of atoms that are usually arranged in repeating units. The individual basic units of structure from which a polymer is constructed are known as monomers. The first two synthetic fibers, nylon and rayon, were produced in the early 1900s. Rayon was created in 1910 in a laboratory from chopped up pieces of cellulose fiber from wood. The cellulose was then chemically treated to make it softer and forced through a special strainer known as a spinneret which produced long threads of fiber. Because Rayon is made from cellulose which is a natural product, it is not a true synthetic fiber, but rather a regenerated fiber. Regenerated fibers are man made from regenerated cellulose which comes from natural substances such as wood or cotton pulp. Examples of regenerated fibers include acetate and triacetate. True synthetic fibers are completely manufactured using polymers and includes fibers such as nylon, polyester, and acrylics. Nylon was first manufactured in 1939 by Dupont. It is the second most popular synthetic fiber, with polyester being the most common synthetic fiber. Synthetic fibers are manufactured by melting small pieces of the material and forcing them through spinnerets.

Synthetic fibers are generally more uniform and smooth along the edges compared to natural fibers.

Identification and Comparison of Man-Made Fibers

Fabrics that have been torn and can be pieced together like pieces of a puzzle are easy to match and classify as individual evidence. When that is not possible, microscopic comparison of color and diameter is necessary as well as comparison of lengthwise striations and pitting on the surface of a fiber. Viewing the cross sections of fibers is also generally helpful.

The combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics.

The physical characteristics of fibers may be examined by the following:

• Counting the number of filaments

• Calculating the density of the fiber

• Evaluating the Refraction Index of the fiber

• Checking the fiber for fluorescence

The chemical characteristics of fibers may be examined in the following ways:

• Oxidation tests: This involves burning the fiber to evaluate the ash, behavior in the flame and any smells associated with the fiber.

• pH Testing

• Evaluating any residues or component parts within synthetic fibers

• Chemical Decomposition tests: Treating fibers with strong acids, bases or solvents

These tests would be conducted with the evidence samples and compared with the results of standard samples from the lab or common materials. A unique fiber on a victim matched with the same type unique fiber on a suspect, or in the suspect's possession, can be compelling evidence if the fiber characteristics match in all of the above testing! Even though fiber evidence is generally considered class evidence as mentioned previously, fibers that still have matching characteristics after numerous sets of testing is very useful evidence in an investigation! This is why so much care is taken in the collection and analysis of hair and fiber evidence.

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Collection of Fiber Evidence

Collection of Fiber Evidence

When collecting fiber evidence for analysis, care must be taken not to inadvertently lose the often tiny fibers or to cross-contaminate with other fibers from personnel at the scene. Forensic investigators follow strict protocols on how to collect fiber evidence at the scene to avoid possible contamination or loss of evidence. Some of the guidelines include:

In the end, the significance of fiber evidence, as well as the collection method, is dictated by the circumstances of the case.

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