<CHAP NUM="8" ID="CH.00.008">chapter 8
<FM><TTL>Hairs, Fibers, and Paint</TTL>
<KTSET><TTL>Key Terms</TTL>
<KT>anagen phase</KT>
<KT>catagen phase</KT>
<KT>cortex</KT>
<KT>cuticle</KT>
<KT>follicular tag</KT>
<KT>macromolecule</KT>
<KT>manufactured fibers</KT>
<KT>medulla</KT>
<KT>mitochondrial DNA</KT>
<KT>molecule</KT>
<KT>monomer</KT>
<KT>natural fibers</KT>
<KT>nuclear DNA</KT>
<KT>polymer</KT>
<KT>telogen phase</KT></KTSET>
<OBJSET><TTL>Learning Objectives</TTL>
<P>After studying this chapter you should be able to:
<OBJ><P><INST>< </INST>Recognize and understand the cuticle, cortex, and medulla areas of hair</P></OBJ>
<OBJ><P><INST>< </INST>List the three phases of hair growth</P></OBJ>
<OBJ><P><INST>< </INST>Appreciate the distinction between animal and human hairs</P></OBJ>
<OBJ><P><INST>< </INST>List hair features that are useful for the microscopic comparison of human hairs</P></OBJ>
<OBJ><P><INST>< </INST>Explain the proper collection of forensic hair evidence</P></OBJ>
<OBJ><P><INST>< </INST>Describe and understand the role of DNA typing in hair comparisons</P></OBJ>
<OBJ><P><INST>< </INST>Understand the differences between natural and manufactured fibers</P></OBJ>
<OBJ><P><INST>< </INST>List the properties of fibers that are most useful for forensic comparisons</P></OBJ>
<OBJ><P><INST>< </INST>Describe the proper collection of fiber evidence</P></OBJ>
<OBJ><P><INST>< </INST>List the most useful examinations for performing a forensic comparison of paint</P></OBJ>
<OBJ><P><INST>< </INST>Describe the proper collection and preservation of forensic paint evidence</P></OBJ></P></OBJSET></FM>
<CASE NUM="1" TY="CS"><TTL>Jeffrey McDonald: Fatal Vision</TTL>
<P>The grisly murder scene that confronted police on February 17, 1970, is one that cannot be wiped from memory. Summoned to the Fort Bragg residence of Captain Jeffrey McDonald, a physician, police found the bludgeoned body of McDonald’s wife. She had been repeatedly knifed and her face was smashed to a pulp. McDonald’s two children, ages 2 and 5, had been brutally and repeatedly knifed and battered to death. Suspicion quickly fell on McDonald. To the eyes of investigators, the murder scene had a staged appearance. McDonald described a frantic effort to subdue four intruders who had slashed at him with an ice pick. However, the confrontation left McDonald with minor wounds and no apparent defense wounds on his arms. McDonald then described how he had covered his slashed wife with his blue pajama top. Interestingly, when the body was removed blue threads were observed under the body. In fact, blue threads matching the pajama top turned up throughout the house—nineteen in one child’s bedroom, including one beneath her fingernail, and two in the other child’s bedroom. Eighty-one blue fibers were recovered from the master bedroom, and two were located on a bloodstained piece of wood outside the house. Later forensic examination showed that the forty-eight ice pick holes in the pajama top were smooth and cylindrical, a sign that the top was stationary when it was slashed. Also, folding the pajama top demonstrated that the forty-eight holes actually could have been made by twenty-one thrusts of an ice pick. This coincided with the number of wounds that McDonald’s wife sustained. As described in the book <ITAL>Fatal Vision,</ITAL> which chronicled the murder investigation, when McDonald was confronted with adulterous conduct, he replied, “You guys are more thorough than I thought.” McDonald is currently serving three consecutive life sentences.</P></CASE>
<BM><P>The trace evidence transferred between individuals and objects during the commission of a crime, if recovered, often corroborates other evidence developed during the course of an investigation. Although in most cases physical evidence cannot by itself positively identify a suspect, laboratory examination may narrow the origin of such evidence to a group that includes the suspect. Using many of the instruments and techniques described in the previous three chapters, the crime laboratory has developed a variety of procedures for comparing and tracing the origins of physical evidence. This and the forthcoming chapters discuss how to apply these techniques to the analysis of the types of physical evidence most often encountered at crime scenes. We begin with a discussion of hairs, fibers, and paint.</P>
<H1>Morphology of Hair</H1>
<P>Hair is encountered as physical evidence in a wide variety of crimes. However, any review of the forensic aspects of hair examination must start with the observation that it is not yet possible to individualize a human hair to any single head or body through its morphology. Over the years, criminalists have tried to isolate the physical and chemical properties of hair that could serve as individual characteristics of identity. Partial success has finally been achieved by isolating and characterizing the DNA present in hair. The importance of hair as physical evidence cannot be underemphasized. Its removal from the body often denotes physical contact between a victim and perpetrator and hence a crime of a serious or violent nature. When hair is properly collected at the crime scene and submitted to the laboratory along with enough standard/reference samples, it can provide strong corroborative evidence for placing an individual at a crime site.</P>
<P>The first step in the forensic examination of hair logically starts with its color and structure, or morphology, and, if warranted, progresses to the more detailed DNA extraction, isolation, and characterization.</P>
<P>Hair is an appendage of the skin that grows out of an organ known as the <ITAL>hair follicle</ITAL>. The length of a hair extends from its root or bulb embedded in the follicle, continues into the shaft, and terminates at the tip end. The shaft, which is composed of three layers—the <KT>cuticle</KT><SIDEIND NUM="1" ID="MN2.08.001"/>, <KT>cortex</KT><SIDEIND NUM="2" ID="MN2.08.002"/>, and <KT>medulla</KT><SIDEIND NUM="3" ID="MN2.08.003"/>—is subjected to the most intense examination by the forensic scientist (see <LINK LINKEND="FG.08.001">Figure <FIGIND NUM="1" ID="FG.08.001"/>8–1</LINK>).</P>
<H3>Cuticle.<INST> </INST></H3><P>Two features that make hair a good subject for establishing individual identity are its resistance to chemical decomposition and its ability to retain structural features over a long period of time. Much of this resistance and stability is attributed to the cuticle or outside covering of the hair. The cuticle is formed by overlapping scales that always point toward the tip end of each hair. The scales form from specialized cells that have hardened <ITAL>(keratinized)</ITAL> and flattened in progressing from the follicle. The scales of most animal hair can best be described as looking like shingles on a roof. Although the scale pattern is not a useful characteristic for individualizing human hair, the variety of patterns formed by animal hair makes it an important feature for species identification. <LINK LINKEND="FG.08.002">Figure <FIGIND NUM="2" ID="FG.08.002"/>8–2</LINK> shows the scale patterns of some animal hairs and of a human hair as viewed by the scanning electron microscope. Another method of studying the scale pattern of hair is to make a cast of its surface. This is done by embedding the hair in a soft medium, such as clear nail polish or softened vinyl. When the medium has hardened, the hair is removed, leaving a clear, distinct impression of the hair’s cuticle, ideal for examination with a compound microscope.</P>
<H3>Cortex.<INST> </INST></H3><P>Contained within the protective layer of the cuticle is the cortex. The cortex is actually made up of spindle-shaped cortical cells aligned in a regular array, parallel to the length of the hair. The cortex derives its major forensic importance from the fact that it is embedded with the pigment granules that give hair its color. The color, shape, and distribution of these granules provide important points of comparison among the hairs of different individuals.</P>
<P>The structural features of the cortex are examined microscopically after the hair has been mounted in a liquid medium with a refractive index close to that of the hair. Under these conditions, the amount of light reflected off the hair’s surface is minimized, and the amount of light penetrating the hair is optimized.</P>
<H3>Medulla.<INST> </INST></H3><P>The medulla is a collection of cells that looks like a central canal running through a hair. In many animals, this canal is a predominant feature, occupying more than half of the hair’s diameter. The <ITAL>medullary index</ITAL> measures the diameter of the medulla relative to the diameter of the hair shaft and is normally expressed as a fraction. For humans, the index is generally less than one-third; for most other animals, the index is one-half or greater.</P>
<P>The presence and appearance of the medulla vary from individual to individual and even among the hairs of a given individual. Not all hairs have medullae, and when they do exist, the degree of medullation can vary. In this respect, medullae may be classified as being continuous, interrupted, fragmented, or absent (see <LINK LINKEND="FG.08.003">Figure <FIGIND NUM="3" ID="FG.08.003"/>8–3</LINK>). Human head hairs generally exhibit no medullae or have fragmented ones; they rarely show continuous medullation. One noted exception is the Mongoloid race, whose members usually have head hairs with continuous medullae. Also, most animals have medullae that are either continuous or interrupted.</P>
<P>Another interesting feature of the medulla is its shape. Humans, as well as many animals, have medullae that give a nearly cylindrical appearance. Other animals exhibit medullae that have a patterned shape. For example, the medulla of a cat can best be described as resembling a string of pearls, whereas members of the deer family show a medullary structure consisting of spherical cells occupying the entire hair shaft. <LINK LINKEND="FG.08.004">Figure <FIGIND NUM="4" ID="FG.08.004"/>8–4</LINK> illustrates medullary sizes and forms for a number of common animal hairs and a human head hair.</P>
<P>A searchable database on CD-ROM of the thirty-five most common animal hairs encountered in forensic casework is commercially available.<FNIND NUMBER="1"/>1 This database allows an examiner to rapidly search for animal hairs based on scale patterns and/or medulla type using a PC. A typical screen presentation arising from such a data search is shown in <LINK LINKEND="FG.08.005">Figure <FIGIND NUM="5" ID="FG.08.005"/>8–5</LINK><SIDEIND NUM="1" ID="MN1.08.001"/>.</P>
<H3>Root.<INST> </INST></H3><P>The root and other surrounding cells within the hair follicle provide the tools necessary to produce hair and continue its growth. Human head hair grows in three developmental stages, and the shape and size of the hair root is determined by the growth phase in which the hair happens to be. The three phases of hair growth are the <KT>anagen</KT><SIDEIND NUM="4" ID="MN2.08.004"/>, <KT>catagen</KT><SIDEIND NUM="5" ID="MN2.08.005"/>, and <KT>telogen phases</KT><SIDEIND NUM="6" ID="MN2.08.006"/>. In the anagen phase, which may last up to six years, the root is attached to the follicle for continued growth, giving the root bulb a flame-shaped appearance [<LINK LINKEND="FG.08.006">Figure <FIGIND NUM="6" ID="FG.08.006"/>8–6(a)</LINK>]. When pulled from the root, some hairs in the anagen phase have a <KT>follicular tag</KT><SIDEIND NUM="7" ID="MN2.08.007"/>. With the advent of DNA analysis, this follicular tag is important for individualizing hair. Hair continues to grow, but at a decreasing rate, during the catagen phase, which can last anywhere from two to three weeks. In the catagen phase, roots typically take on an elongated appearance [Figure 8–6(b)] as the root bulb shrinks and is pushed out of the hair follicle. Once hair growth ends, the telogen phase begins and the root takes on a club-shaped appearance [Figure 8–6(c)]. Over two to six months, the hair is pushed out of the follicle, causing the hair to be naturally shed.</P>
<H1>Identification and Comparison of Hair</H1>
<P>Most often the prime purpose for examining hair evidence in a crime laboratory is to establish whether the hair is human or animal in origin or to determine whether human hair retrieved at a crime scene compares with hair from a particular individual. Although animal hair can normally be distinguished from human hair with little difficulty, human hair comparisons must be undertaken with extreme caution and with an awareness of hair’s tendency to exhibit variable morphological characteristics, not only from one person to another but also within a single individual.</P>
<P>A careful microscopic examination of hair reveals morphological features that can distinguish human hair from animal hair. The hair of various animals also differs enough in structure that the examiner can often identify the species. Before reaching such a conclusion, however, the examiner must have access to a comprehensive collection of reference standards and the accumulated experience of hundreds of prior hair examinations. Scale structure, medullary index, and medullary shape are particularly important in hair identification.</P>
<P>The most common request when hair is used as forensic evidence is to determine whether hair recovered at the crime scene compares to hair removed from a suspect. In most cases, such a comparison relates to hair obtained from the scalp or pubic area. Ultimately, the evidential value of the comparison depends on the degree of probability with which the examiner can associate the hair in question with a particular individual.</P>
<P>In making a hair comparison, a comparison microscope is an invaluable tool that allows the examiner to view the questioned and known hair together, side by side. Any variations in the microscopic characteristics will thus be readily observed. Because hair from any part of the body exhibits a range of characteristics, it is necessary to have an adequate number of known hairs that are representative of all its features when making a comparison.</P>
<P>In comparing hair, the criminalist is particularly interested in matching the color, length, and diameter. Other important features are the presence or absence of a medulla and the distribution, shape, and color intensity of the pigment granules in the cortex. A microscopic examination may also distinguish dyed or bleached hair from natural hair. A dyed color is often present in the cuticle as well as throughout the cortex. Bleaching, on the other hand, tends to remove pigment from the hair and to give it a yellowish tint. If hair has grown since it was last bleached or dyed, the natural-end portion will be quite distinct in color. An estimate of the time since dyeing or bleaching can be made because <ITAL>hair grows approximately one centimeter per month.</ITAL> Other significant but less frequent features may be observed in hair. For example, morphological abnormalities may be present due to certain diseases or deficiencies. Also, the presence of fungal and nit infections can further link a hair specimen to a particular individual.</P>
<P>While microscopic comparison of hairs has long been accepted as an appropriate approach for including and excluding questioned hairs against standard/reference hairs, many forensic scientists have long recognized that this approach is very subjective and is highly dependent on the skills and integrity of the analyst, as well as the hair morphology being examined. However, until the advent of DNA analysis, the forensic science community had no choice but to rely on the microscope to carry out hair comparisons. Any lingering doubts about the necessity of augmenting microscopic hair examinations with DNA analysis evaporated with the publication of an FBI study describing significant error rates associated with microscopic comparison of hairs.<FNIND NUMBER="2"/>2 Hair evidence submitted to the FBI for DNA analysis between 1996 and 2000 was examined both microscopically and by DNA analysis. Approximately 11 percent of the hairs (9 out of 80) in which FBI hair examiners found a positive microscopic match between questioned and standard/reference hairs were found to be nonmatches when they were later subjected to DNA analysis. The course of events is clear; microscopic hair comparisons must be regarded by police and courts as presumptive in nature and all positive microscopic hair comparisons must be confirmed by DNA determinations.<BOXIND NUM="1" ID="BX1.08.001"/></P>
<P>A number of questions may be asked to further ascertain the present status of forensic hair examinations.</P>
<BOX NUM="1" TY="BX1" ID="BX1.08.001"><SUPTTL>Forensics at Work</SUPTTL>
<TTL>The Central Park Jogger Case Revisited...
Januszek66