Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION. Jones & Bartlett Learning, LL NOT FOR SALE OR DISTRIBUT

Transcription

1 Darren Baker/ShutterStock, Inc...

2 The Microscope and Forensic CHAPTER 4 Identification of Hair, F Fibers, and Paint OBJECTIVES FEATURES On the Crime Scene Serial Murderer Everett Bell Identified F DISTRIBUT by Nubs In this chapter you should gain an understanding of: The parts of a compound microscope and how it works The use of a comparison microscope to compare two objects The Jones large working distance and the larger depth of field afforded by the stereomicroscope Differentiation of amorphous and crystalline materials by use of a polarized light microscope The structure of hair and the microscopy techniques used to identify human hair The characteristics of natural fibers, humanmade fibers, and the fabrics made with both F types of fibers The composition of different types of paints and how paint samples are characterized The use of microspectrophotometers and scanning electron microscopes in the forensic lab See You in Court Back At the Crime Lab WRAP UP Chapter Spotlight Key Terms Putting It All Together Further Reading..

3 YOU ARE THE FENSIC SCIENTIST The microscopic techniques used to investigate trace fiber and hair evidence focus on their morphology. Morphology is a term that is used to describe the size, shape, and color of the evidence. The methods employed Jones & for Bartlett morphological LL comparisons of questioned F and control samples often are used to show that two samples do not F match. Indeed, more DISTRIBUT suspects are exonerated by morphological comparison than are implicated by it. Only very rarely will the examiner be able to confirm that the individual who left behind the questioned trace sample was the same person who is the source of the control sample. The utility & of Bartlett morphological comparison methods is limited because morphology Jones & often Bartlett is not capable of individualizing hair and fibers. When two samples are similar enough to have originated from the same person, additional tests must be performed to establish their origin. 1. A bank was robbed by a man wearing a black ski mask. In a subsequent search of the bank parking lot, police recovered a black ski mask. What trace evidence might be present? How should that evidence be investigated? 2. The examiners at the forensic lab found a short, brown Jones beard & hair Bartlett inside the ski mask. Should the investigators focus their search on men with brown beards? Introduction During the search of a crime scene, investigators will inevitably encounter many types of physical evidence. Although the search may initially focus on large objects that may prove to be evidence, trace evidence must not be overlooked. Trace evidence F is a generic term used to describe small, often microscopic, objects that are readily transferred between people and places. The range of objects falling into the category of trace evidence is enormous and can include hair, fibers, glass, soil, feathers, pollen, dust, and paint. F In 1932, with a borrowed microscope and a few other pieces of basic equipment, the Federal Bureau of Investigation (FBI) established its technical laboratory in Washington, DC. The microscopic comparison of fibers and hairs was among considered a wonder. the first examinations F performed by this laboratory. Since then, forensic laboratories (including Refraction the FBI laboratory) have greatly expanded their capacity to handle trace evidence thanks to the development of modern analytical instruments. Even with much more sophisticated instruments available, F however, forensic scientists today usually begin their examination of trace evidence with a microscope. This chapter describes the various types of microscopes available in forensic laboratories that are used to examine hairs and F fibers. Magnifying Small Details Forensic scientists often are F confronted with the DISTRIBUT need to analyze many different types of materials obtained during criminal investigations. The identification or comparison of minuscule traces of a wide range of materials is a common occurrence in a modern crime F lab. The earliest detectives including the fictional Sherlock Holmes used magnifying glasses to carefully examine evidence in the field and microscopes to study objects brought to their laboratories. & Early Bartlett crime labs relied almost entirely on the F light microscope for examining minute details of evidence that were not visible to the naked eye. This kind of a microscope offered less than 10 times (10 ) magnification capabilities but was still A magnifying glass is a lens that is thicker in the middle than at the edge. It makes objects appear larger than they are by refracting (bending) light rays as they repeatedly F pass through the air and back through the lens. When light passes at an angle through the interface between two transparent media (e.g., air and glass) that have different densities, an abrupt change in direction that is, refrac- F tion of the beam is observed as a consequence of 84 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint..

4 FIGURE 4-1 The glass on the left shows the apparent position of a straw in water as seen by the eye. Refraction makes it appear that the straw is broken at the surface of the water. the difference in the velocity of the light in the two media. The phenomenon of refraction is commonly observed with an object F that is immersed in a glass of water. For example, when a glass of water contains a straw ( FIGURE 4-1 ), refraction makes it appear that the straw is broken at the surface of the water. As the & rays Bartlett of light leave the water and enter the air, F their velocity increases, causing them to be refracted. How much light bends (and thus the focal length) depends on the change in the refractive index (η) as the light enters and leaves the magnifying glass. The refractive index is a ratio & of Bartlett the velocity of light in a vacuum to its velocity F in any other medium: Simple Magnifying Lens Velocity of light in a vacuum Refractive Index = η = Velocity of light in a denser medium & Subject Bartlett LL The refractive index is 1.0 for F air and 1.33 for water Virtual at 25 C. A typical glass has a refractive index of Image about 1.4 (a difference of 0.4 for light passing from air to glass). To use a magnifying glass to examine an object, you look through the lens ( FIGURE 4-2 ). The magnified F image is called the virtual image. As the lens is moved closer to the eye, the virtual image increases in size by 5 to 10 times. Higher magnification requires two lenses that are at fixed distances from each other in a hollow tube, a setup FIGURE 4-2 As light passes through a magnifying lens, the known as a compound microscope. image of the bullet becomes magnified... Retina Refraction 85

5 Types of Microscopes Ocular Lens F A microscope has at least two lenses: an objective Mirror lens and an ocular lens or eyepiece ( FIGURE 4-3 ). The objective lens, which is the lower lens in the Head hollow tube, produces a real image a magnified and inverted version Jones of & the Bartlett object being examined. The real image is F then viewed through the Turret LL Arm ocular lens (the smaller lens at the other end of the hollow tube in the eyepiece), producing a Objective Lens virtual image in the brain of the viewer. The virtual Stage image is a magnified image produced in the Condenser Focus viewer s mind of the real image; it has the same Knob orientation as the real image, but its magnification exceeds the magnification of the real image by the ocular lens ( FIGURE 4-4 ). The magnification power Illuminator Base of a microscope is greater than that of a magnifying glass because the former device has two lenses. The FIGURE 4-3 A typical compound microscope uses a light F magnifying power of a microscope is determined F bulb to illuminate the specimen (light microscope). by multiplying the power of the objective lens by the power of the ocular lens. A compound microscope can magnify objects up to 1,500 times. depends on the wavelength of the light used to A compound microscope even one with perfect lenses using a tungsten light bulb to illuminate units of micrometers (µm; also known as microns), illuminate the object. Wavelength is measured in the object has limitations, however. In particular, where 1 µm is equal to mm. The wavelength its ability to distinguish extremely small objects of white light (which is typically used to illuminate FIGURE 4-4 The passage of light through two lenses forms a virtual image of the object as seen by the eye. 86 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint..

6 objects in compound microscopes) is 0.55 µm, There are several types of electric lighting and a compound microscope can distinguish (illuminators) for microscopes. Tungsten is the F objects that are roughly one-half of that size (i.e., least F expensive electric illumination; it is also hotter and less bright than the other kinds of illumi µm). Smaller objects if they are seen at all may appear as a blur. To compensate for this nators. Fluorescent provides cooler and brighter shortcoming, some compound microscopes use light than tungsten. This is beneficial when you are blue light (which has a shorter & wavelength Bartlett than viewing slides for long periods of time or & when Bartlett you LL white light) to illuminate the F object of interest. are observing live specimens, such F as protozoa. DISTRIBUT Five types of microscopes are typically used for Halogen provides the very brightest illumination. forensic examinations: In the condenser, the light rays from the illuminator are focused through a lens in the center of 1. Compound microscope the stage and onto the specimen. The condenser 2. Comparison & microscope Bartlett has an iris diaphragm that can be opened or closed 3. Stereoscopic F microscope to regulate the amount F of light passing into the 4. Polarizing microscope condenser. 5. Microspectrophotometer The eyepiece is the part of the microscope that Each of these microscopes has a specific function you look through. The objective is the second lens & that Bartlett makes it very effective for obtaining certain of the microscope. Compound microscopes have a F types of information. The scanning electron microscope (SEM), which can provide magnification of nosepiece F with a rotating objective turret, which allows you to change the objective lens and amplification power. The viewed image is magnified by more than 100,000 times, also is occasionally used for forensic examination of evidence. both the objective and the eyepiece lens. Thus the total magnification is equal to the product of the magnifying power of the two lenses. For example, Compound Microscopes if the eyepiece lens has a magnification F of 10 and DISTRIBUT The mechanical system of a compound microscope the objective lens has a magnification of 40, the has six important parts: total magnification will be the product of the two Base: The stand on which the microscope sits. lenses magnifications: = 400. Forensic Arm: A metal & piece Bartlett that supports the tube body examiners typically use & a Bartlett 10 eyepiece with nosepiece that contains F a 4, 10, 25, or 40 objective of the microscope. F It is also used as a handle to pick up the microscope. lens, providing magnification of 40, 100, 250, or 400, respectively. Body tube: A hollow tube that holds the objective lens at the lower end and the eyepiece lens Each objective lens is stamped with a numerical aperture (NA). As the NA doubles, the lens is at the upper end. Light passes from the objective lens through the body tube to the eyepiece, as distant from able to & resolve Bartlett details that are half F where it is observed by the eye. each F other (twice as close to each other). The NA is effectively an index of the ability of the objective lens to resolve fine detail. The higher the NA Stage: The platform that supports the specimen. The specimen is placed on a glass slide (up to about 1000 the NA), the more detail the that is clipped into place on the stage. The microscope can discern. Anything beyond 1000, x- and y-axis stage control & knobs Bartlett are used to however, is considered empty magnification that move the slide back and F forth under the objective lens. doesn t add anything to the clarity of the image. The forensic examiner must balance the microscope s magnifying power with both the field of Coarse adjustment: A knob that focuses the microscope on the specimen by raising and view and the depth of focus. The field of view is lowering the & body Bartlett tube of the microscope. the area that the Jones forensic & examiner Bartlett sees when looking through the eyepiece. F As the magnifying power Fine adjustment: F A knob that adjusts the height of the body tube in smaller increments so the increases, the field of view shrinks. The examiner specimen can be brought into fine focus. should start with a low magnification. After taking in this (relatively) big picture, the examiner The optical system has four fundamental parts: & the Bartlett illuminator, the condenser, the eyepiece, and should & switch Bartlett to a higher-power objective lens to F the objective. scrutinize F particular parts of the specimen more.. Types of Microscopes 87

7 on the CRIME SCENE Serial Murderer F Everett Bell Identified by Nubs On August 22, 1995, the body & of Bartlett 8-year-old Sandra was discovered by police in a wooded area near & her Bartlett church in LL southern Michigan. The F child had been brutally assaulted before she died of strangulation. Her F bicycle was found DISTRIBUT near her partially hidden body. Police cordoned off the wooded area and the adjacent church parking lot to perform a detailed search of the area. Fingerprints were taken from the victim s body and from the bicycle. The coroner discovered material under Sandra s fingernails, on her abdomen, and on her hands. Vaginal and rectal Jones swabs & and Bartlett analysis of her clothing revealed no biological material other & than Bartlett her own. Furthermore, the bicycle provided no incriminating fingerprint evidence. However, hair and fibers were found on the victim. The police launched a major investigation, canvassing the neighborhood around the church. They found that Everett Bell, a local resident and an employee of a Hardee s restaurant, was seen in the area around nightfall riding his bicycle. Bell s employer revealed that Bell had been sent home early from work that day. The Hardee s manager gave police Bell s work pants, shirt, and cap. The FBI laboratories found blue cotton fibers under Jones Sandra s fingernails. When they were examined under a F microscope, it was clear that these fibers matched the blue F cotton fibers from the suspect s shirt. Blue and green fibers found on Sandra s clothes also matched those from the shirt. In addition, a dark blue-gray polyester fiber matching the fibers of the suspect s pants matched fibers found on the rectal swab. Of particular interest, the sample from the victim contained nubs ; the end of the fiber was melted during manufacture into bulbs that are called nubs. The nubs Jones that were lifted with tape from Bell s shirt matched the nubs lifted from the & surface Bartlett of the LL victim s shirt. Hardee s employees were given particular shirts manufactured by WestPoint Stevens Alamac Knits. Bell s shirt was a short-sleeve polo shirt that Hardee s had recently replaced with a striped shirt. Therefore, few of the solid shirts were still being worn by employees. Tape applied to the surface of Bell s shirt removed a significant number of the nubs that proved to be identical to nubs found on the victim s clothes, establishing physical contact between Jones the victim and the suspect. Bell F later confessed to Sandra s murder as well as to five other rapes and F at least nine other murders. closely. The examiner should also adjust the depth is essentially two compound microscopes that are of focus (the thickness of the region in focus, connected by an optical bridge that is, a series of F which affects the clarity of the image) as necessary. As with the field of view, when the magnify- objective lenses. The comparison microscope has a F mirrors and lenses that link the two microscopes ing power increases, the depth of focus decreases. single eyepiece through which the forensic examiner sees the images from both compound micro- Thus both field of view and depth of focus decrease as magnifying power increases. As a consequence, high powers scopes placed side by side. F of magnification sacrifice Comparison microscopes F that compare semitransparent hairs and fibers are lighted from below DISTRIBUT both the size of the area in view and the thickness of the region in focus. Low powers of magnification sacrifice detail within the region under exami- designed to compare bullets, bullet cartridges, and the stage. Other comparison microscopes are nation and in focus. For this reason, a trade-off is other opaque objects ( FIGURE 4-5 ). Because these necessary when using a compound microscope. specimens do not transmit light, illumination from below the stage F is not possible; instead, optical Comparison Microscopes microscopes for viewing these items are equipped To compare two specimens, such as evidence taken with a vertical or reflected illumination system from a crime scene with a reference sample taken ( FIGURE 4-6 ). from a suspect, the forensic examiner often uses a Jones & An Bartlett experienced examiner will mount the evidence F comparison microscope. A comparison microscope F on the same side for all comparisons. For 88 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint..

8 Courtesy of Leica Microsystems, Inc. Courtesy of Leica Microsystems, Inc. FIGURE 4-5 This comparison microscope is used to compare the marks or scratches on a bullet recovered from a crime scene to a test bullet fired from a gun suspected of being a murder weapon. Ocular Lens Objective Lens Light Source Light Source FIGURE 4-7 Although it will magnify only 125x, the stereomicroscope is the most commonly used microscope in forensics. The stereoscopic microscope has several features that make it particularly easy to use. This Working F Distance device has two eyepieces, which make it more comfortable for the viewer. It also produces a three-dimensional image that is presented in a Stage right-side-up, frontward orientation (unlike the upside-down, backward orientation of the image produced F by a compound microscope). Its large FIGURE 4-6 This microscope is lit from above and is used to working distance, which is the distance between examine opaque materials. the objective lens and the specimen, means that the forensic examiner can use this device to view large items. Finally, the stereoscopic microscope instance, an examiner who is right handed should can be lighted either from below, to illuminate always place the evidence on F the right microscope semitransparent objects, or vertically F from above, DISTRIBUT stage and the reference material on the left stage. to illuminate opaque objects. When this is done without fail, the evidence and the standard reference will not be confused. Polarizing Microscopes The compound microscope has been used to determine the types of F minerals present in geological Stereoscopic F Microscopes The stereoscopic microscope ( FIGURE 4-7 ) is the samples for more than 100 years. Minerals whose most commonly used microscope in crime laboratories. Although it is able to magnify images by as amorphous materials. Minerals whose atoms atoms are arranged in random order are classified & only Bartlett 10 to 125, many types of physical evidence are arranged in a distinct order are classified as F are routinely examined under low magnification. crystalline F materials... Types of Microscopes 89

9 By observing how light interacts with thin sections of the minerals, the forensic examiner can classify minerals and classification is the first step in F A. F forensic identification. The classification techniques described here rely on the fact that light traveling through the minerals in different directions will behave differently, but predictably. These differences can be detected with F a polarizing microscope. To examine and classify a mineral, the sample must B. be dry and thin enough to be placed on a microscope slide under a cover slip. If the material is too thick, a portion can be shaved off with a scalpel. Isotropic materials such as gases, liquids, and cubic F crystals have the same optical properties when observed from any direction. Because plane as it passes through the first polarizer, and it will FIGURE 4-8 (A) Light F from a light bulb is polarized in one reach the eye only if the second polarizer is in the same isotropic materials have only one refractive index, position. (B) When the second polarizer is rotated, it cuts they appear the same when light passes through off the light and stops its transmission. them from different directions. By contrast, anisotropic (or birefringent) materials such as quartz, F is rotated, less plane-polarized light is transmitted calcite, and asbestos are crystalline. In anisotropic minerals, the arrangement of atoms is not the through the second lens, and, at a rotation of 90, no light is transmitted ( FIGURE 4-8B ). same in all directions. Thus, when an anisotropic material is examined, the arrangement of atoms in Polarized Light Microscopy the substance appears to change as the direction of observation changes. F Photons of light passing A polarizing microscope includes F two polarizing DISTRIBUT through asbestos fibers from different directions filters: the polarizer lens, which is fixed in place will encounter different electrical neighborhoods, below the specimen, and the analyzer lens, which is which in turn will affect the path and time of travel located above the specimen ( FIGURE 4-9 ). The sample of the Jones light & beam Bartlett in different ways. Besides F providing information on the shape, color, and size of different minerals, polarized light microscopy can distinguish between isotropic and anisotropic materials. This technique is used to identify the presence of certain minerals and their anisotropic properties. Plane-Polarized Light According to the wave theory of light, light waves oscillate (vibrate) at Jones right angles to the direction which the light is traveling F through space. The oscillations occur in all planes that are perpendicular to the path traveled by the light. These oscillations may be produced by a light bulb and viewed by an observer looking directly into the beam ( FIGURE 4-8A ). If the Jones beam & of Bartlett light is passed through a sheet of Polaroid F material, the light that is transmitted through the Polaroid sheet oscillates in one plane only. Such light is called plane-polarized light. If a second Polaroid lens is inserted before your eye, that lens must be aligned in a parallel plane so that planepolarized F light is passed. If the second Polaroid lens 90 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint.. FIGURE 4-9 A polarizing microscope includes two polarizing filters: the polarizer lens and the analyzer lens. Courtesy of Leica Microsystems, Inc.

10 stage, which is placed between the two filters, can completed, the analyst can then hone in on small be easily rotated. details at higher magnification. When an interesting F characteristic is identified, its morphology can F Besides information about the gross fiber morphology and color of the sample, analysis of plane- be compared with that of a reference material and polarized light can determine whether the sample its optical properties identified via a polarizing exhibits pleochroism. Pleochroism is the property microscope. that causes a substance to show & different Bartlett absorption colors when it is exposed F to polarized light been attached to spectrophotometers. F In a spectro- DISTRIBUT In the past 2 decades, microscopes Jones have also LL coming from different directions. The observed photometer, a lamp emits radiation either ultraviolet (UV) or infrared (IR) that passes through a colors change with the orientation of the crystal and can be seen only with plane-polarized light. sample. The sample absorbs some of this light, and As the sample stage is rotated, these substances the rest passes to the spectrophotometer. There, change color. the light from the sample is separated according Polarized F light microscopy also is used to identify human-made fibers and paint. If a fiber is col- a rainbow), and the spectrum formed is observed to its wavelength (the F visible range light looks like lected from a victim and placed on a microscope with a detector. Such analysis (spectroscopy) is slide, it may be difficult to tell one type of fiber used to elucidate the composition of unknown & from Bartlett another. If it is a glass fiber, however, its materials in many different fields. Spectroscopy F color will not change as the microscope stage is can F also be used to match compounds, measure rotated. That is, because glass fibers are isotropic, concentrations, and determine physical structures. they are unaffected by rotation under polarized A microspectrophotometer combines the light. Other human-made fibers are anisotropic capabilities of a spectrophotometer with those of a and change colors as the stage is rotated. It is microscope. The microscope magnifies the image an easy matter to compare the pleochroism of a of the specimen for the spectrometer and allows the fiber found at a crime scene F to a fiber taken from forensic examiner to analyze extremely F small samples or a small region of a sample. The spectropho- DISTRIBUT the suspect, thereby proving (or disproving) a link between the suspect and the scene. tometer then measures the intensity of light at each wavelength. Microspectrophotometers (also called microspectrometers, microscope spectrophotometers, and microphotometers) F are extremely use- Microspectrophotometers The microscope allows the analyst to look over the ful. In addition to measuring the light absorbed general features of the object being investigated at or transmitted by the sample, a microspectrophotometer can measure the intensity of light low power. Once a general survey of the object is reflected SEE YOU IN COURT In the late 1970s, a wave of child murders occurred Probabilities are difficult to establish in many, if in Atlanta. Wayne Williams was & arrested Bartlett for the offenses, based principally not most, physical evidence cases. Determining the LL on F the carpet fiber evidence likelihood of a match for new car carpet, F for example, would be possible if one knew how many cars DISTRIBUT found on the bodies, which was similar to carpet fibers found in his vehicle. Williams was convicted with that type and color of carpet were sold within and sentenced to life in prison, where he remains a certain distance of the location of interest. Obviously, as the area included increases, the probabilities today. However, Jones & controversy Bartlett has dogged this case since drop. Given that cars generally do not stay confined the moment F the fibers were introduced into evidence. spaces, one would have F to make explicit assumptions Contrary to the practice today, the jury was never to justify the development of a probability statement. told that the fibers were not unique but rather heard No such evidence was employed in the Williams case, that they matched carpet fibers that could be found which is why this conviction remains tainted in the throughout the Atlanta metropolitan area. eyes of many modern forensic scientists... Types of Microscopes 91

11 from a sample, the intensity of light emitted when electron source found in the SEM, travel through a a sample fluoresces, or the intensity of polarized specimen in a way that is similar to a beam of light F light after it has interacted with a sample. F passing through a sample in an optical microscope. Microspectrophotometers have numerous ad- Instead of glass lenses directing light wavelengths vantages over conventional spectrometers. For through a specimen, however, the electron microscope s electromagnetic lenses direct electrons instance, they can easily take spectra of samples as small as 2.5 µm wide while viewing the sample through a specimen ( FIGURE Jones 4-10B &). Bartlett Because the LL directly. The latter feature F allows for more precise measurements of the sample while eliminating wavelength of light, the resolution achieved by the wavelength of electrons is much F smaller than the DISTRIBUT interference from the surrounding material. Also, SEM is many times greater than the resolution because many human-made substances even colorless ones absorb more in the UV region than in can reveal the finest details of structure and the possible with the light microscope. Thus the SEM the visible light and IR regions, microspectrophotometers F are very useful for analysis of synthetic Some of the F electrons striking the surface of the complex surface of synthetic fibers ( FIGURE 4-11 ). fibers (discussed later in this chapter). sample are immediately reflected back toward the To see how this works, suppose that comparison of two fibers one found at a crime scene and trons. An electron detector can be placed above the electron source; these are called backscattered elec- the other taken from a suspect using a polarized sample to scan the surface and produce an image F light microscope indicates that the appearance and F from the backscattered electrons. Other electrons morphology of the two fibers are identical. When that strike the surface of the sample penetrate it; the fibers are analyzed in an IR microspectrophotometer, each produces an IR spectrum. At first is placed beneath the sample. In addition, some of they can be measured by an electron detector that glance, the two spectra appear very similar and the electrons striking the surface cause X-rays to indicate that both fibers Jones are & nylon. Bartlett With a careful be emitted. By measuring the energy of the emitted X-ray, the elemental composition F of the sur- DISTRIBUT LL comparison of the two F spectra, however, small differences become apparent. When these IR spectra face can be determined through a technique called are compared with the IR spectra of known reference fibers, one fiber is found to be nylon-6 and fiber is coated with a dulling agent, such as tita- energy dispersive X-ray spectroscopy (EDX). If a the other nylon-6,6. Although the word nylon is nium dioxide, the EDX will detect its presence. used to F describe an entire class of fibers, there are actually five common nylons sold commercially in the United States: nylon-6,6; nylon-6,12; nylon- Forensic Applications of 4,6; nylon-6; and nylon-12. All nylons share some Microscopy: Hair physical properties (such as solubility in solvent), but some subgroups differ in appearance and Hair & is Bartlett frequently the subject of forensic examination. This analysis has some limitations, however F absorption of dye due to differences in molecular F structure. As this example shows, the microspectrophotometer has the ability to differentiate fibers will not result in definitive identification of the per- namely, forensic examination of an individual hair that fall into the same generic class (nylon) but are son from whom the hair was shed, unless the hair structurally different (nylon-6 versus nylon-6,6). has a tag attached that can Jones be analyzed for DNA. LL At best, a hair s morphology (when compared with Scanning Electron F Microscopes a reference hair) may be consistent with the reference hair; it cannot be said definitively to be a When the evidence available is very small and more magnification is needed, an SEM is often perfect match. Hair does not possess a sufficient used as part of the forensic analysis ( FIGURE 4-10A ). number of unique, individual characteristics to be An SEM can & magnify Bartlett an image 100,000 times and positively associated with a particular person to has a depth F of focus that is more than 300 times the exclusion F of all others. Although hair samples that available with an optical microscope. are commonly used to exclude a suspect, they can An SEM operates on the same basic principle as the polarizing microscope but uses elec- connect the suspect to the crime scene, for exam- be considered only as contributing evidence to trons rather than light to identify properties of Jones ple, & or Bartlett to connect multiple crime scene areas to F the object. Electrons, which are produced in the F each other through transfer of evidence. 92 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint..

12 Courtesy of FEI Company. FIGURE 4-10 (A) A scanning electron microscope (SEM). (B) A schematic diagram of an SEM... Forensic Applications of Microscopy: Hair 93

13 Courtesy of Shara Fessler, Images of Nature at Arizona State University. Cortex Medulla Cuticle Pigment FIGURE 4-12 The shaft of a hair, showing the cuticle, cortex, medulla, pigment, and cortical fusi. Cuticle F The cuticle consists of scales of hardened, flattened, keratinized tissue that overlie the cortex. These scales have a shape and pattern that are unique to the animal species from which they came for example, the cuticle of a cat Jones hair & differs Bartlett from the LL cuticle of a human hair ( FIGURE 4-13 F ). In addition, DISTRIBUT the acidity of modern shampoos can be adjusted to make these scales stand up or lie down. When the scales lie flat, hair reflects light and has an attractive luster think of the attractive model s hair in a shampoo commercial. Jones One way F to observe the scale pattern is to make a cast of the surface. To do so, the forensic examiner presses the hair into a soft material, FIGURE 4-11 (A) Cotton fibers, (B) rayon fibers, and (C) polyester fibers, as seen through a scanning electron such as clear nail polish or soft vinyl. Later, when microscope. the material hardens and the hair is removed, the impression of the cuticle is left behind in the F clear plastic. This plastic will transmit light, so the impression of the cuticle can be examined on Hair Morphology the plastic s surface with a compound microscope Hair is composed primarily of keratin, a very under high magnification. strong protein that is resistant to chemical decomposition and can retain F its structural features for a long time. In fact, even hairs of ancient Egyptian Cortex mummies have been found to retain most of their The cortex consists of an orderly array of spindleshaped cortical cells, which is aligned parallel to structural features. This durability makes hair resistant to physical change and an excellent class the length of the hair. The cortex contains pigment of physical Jones evidence. bodies, which Jones contain the natural dye melanin, and Each F strand of hair grows out of a tubelike cortical fusi, which F are irregular-shaped air spaces structure known as the hair follicle, which is of varying sizes. Cortical fusi are commonly found located within the skin. The shaft of each hair consists of three layers: the cuticle (the outer layer), they may be present throughout the length of the near the root of a mature human hair, although the cortex (the middle layer), and the medulla (the hair. & As Bartlett part of a side-by-side comparison of evidentiary innermost layer) ( FIGURE 4-12 ). F hair samples and reference hair samples, 94 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint Courtesy of Shara Fessler, Images of Nature at Arizona State University. Courtesy of Shara Fessler, Images of Nature at Arizona State University... Cortical Fusi

14 medium that has about the same index of refraction as the hair. This choice minimizes the amount of F reflected light and optimizes the amount of light that penetrates the hair, facilitating the observation of the cortex. Dennis Kunkel Microscopy, Inc./Visuals Unlimited/Corbis M. Kaleb/Custom Medical Stock Photo M. Kaleb/Custom Medical Stock Photo Medulla The medulla consists of one or more rows of darkcolored cells that run lengthwise through the center of the hair shaft. The shape of the medulla may be cylindrical (human) or patterned (animals). The pattern observed Jones is & specific Bartlett to the particular species from which F the hair came. The medulla may be a continuous, fragmented, or interrupted line of dark cells. The medullar ratio (the ratio of the medullar diameter to the hair diameter) for animal hair is generally greater than 0.5; F the medullar ratio for human head hair is generally less than Hair Growth The root of the hair (refer to Jones Figure 4-12) is surrounded by cells that provide all F the necessary DISTRIBUT LL ingredients to generate hair and to sustain its growth. Human hair goes through three developmental stages: the anagenic phase, catagenic phase, and telogenic phase. The size and shape of the hair root are different F in each of these phases ( FIGURE 4-14 ). The anagenic phase is the initial growth phase, during which the hair follicle is actively producing the hair. During this phase, which may last as long as 6 years, the follicle is attached to the root by the dermal F papilla. During the anagenic phase, the hair must be pulled to be lost, in which case it may have a follicular tag. The follicular tag includes cells from the root that contain DNA ( FIGURE 4-15 ). FIGURE 4-13 The cuticle patterns of hairs differ among species of animals, and these patterns serve to distinguish the source Although a human hair itself has Jones no genomic DNA, LL of the hair. (A) Cat hair, (B) dog hair, and (C) sheep wool. it does contain mitochondrial DNA. F The follicular DISTRIBUT tag can be used for DNA typing for either genomic or mitochondrial DNA. the forensic examiner may compare the samples on The catagenic phase is a short period of transition between the anagenic and telogenic phases. the basis of the color, shape, and distribution of their pigment Jones bodies and cortical fusi. It lasts only 2 Jones to 3 weeks. During this phase, hair If hair F has been dyed, dye may sometimes be continues to grow, F but the root bulb shrinks, takes observed in the cuticle and the cortex. If the hair on a club shape, and is pushed out of the follicle. has been bleached, the cortex will be devoid of pigment granules (though it may have a yellow tint). rally becomes loose and falls out. Over a 2- to During the telogenic (final) phase, hair natu- The cortex can be observed with a compound 6-month & period, Bartlett the hair is pushed out of the follicle, F microscope. The hair is usually mounted in a liquid F causing the hair to be naturally shed. The.. Forensic Applications of Microscopy: Hair 95

15 A. former connection, the dermal papilla, is no longer attached to the hair but is assimilated by the F follicle. Hair Hair grows at a constant rate of approximately 1 cm per month. If the shed hair has grown after Inner Root Sheath bleaching or coloring, an estimate of the time since Arrector Pili Muscle chemical treatment can be Jones established by assessing LL Outer Root Sheath the presence (or absence) of color F pigment or dye DISTRIBUT Sebaceous Gland in the cuticle and cortex. Dermal Papilla Comparison of Hair by Microscopy B. When hair evidence is found at the scene of a crime, the forensic examiner must first answer two F Hair questions: (1) F Is the hair human? and (2) does it match the hair of the suspect? Inner Root Sheath Arrector Pili Muscle If the victim is covered with pet hair, a trained forensic examiner should be able to distinguish Outer Root Sheath an & animal Bartlett hair from a human hair with little difficulty. To do so, the examiner will look for matches Sebaceous Gland Basal Lamina F in published reference photos and use microscopy to reveal details of the sample s cuticle (i.e., Germ Dermal Papilla scales), medullar ratio, and medullar pattern. As C. mentioned earlier, these characteristics are often unique to a particular species. Human hair comparison F is a much more difficult task. An examiner typically uses a compar- DISTRIBUT Hair ison microscope to view the evidence hair and Inner Root Sheath Arrector Pili Muscle the known hair side by side. First, the examiner Outer Root Sheath assesses the Jones samples color, length, and diameter. Next, the examiner compares features such as the Sebaceous F Gland shape of the medulla (if present) and the distribution, color, and shape of the pigment granules Dermal Papilla Germ (including whether the hair has been colored or FIGURE 4-14 The three phases of hair growth are (A) the anagen phase, (B) the catagen phase, and (C) the telogen phase. gal & infections, Bartlett or physical damage can also be used bleached). Other abnormalities due to disease, fun- F as a basis for comparison if found in a specimen. The microscopic comparison of human hair has been long accepted by the forensic community as a valid way to include and exclude suspect hairs against reference hairs but only & if the Bartlett examiner LL has the proper training to make F this determination. In 2002, a study by the FBI reported that DISTRIBUT significant error rates were associated with the microscopic comparison of human hairs (Houck & Budlowe, 2002). As part of this study, human hair evidence submitted to the FBI over a 4-year period was subjected F to both standard microscopic examination and DNA analysis. Of the 80 hairs compared, only 9 (approximately 11%) for FIGURE 4-15 The follicular tissue may potentially include DNA, which the FBI examiners found a positive microscopic match between the questioned sample and such as with this forcibly removed head hair with follicular tissue attached. F a reference hair were found not to match by DNA 96 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint M. Kaleb/Custom Medical Stock Photo..

16 The search for hair evidence should begin as soon as it is possible. Hair evidence is easily transferred F to and from the crime scene, perpetrator, and victim. Waiting too long to begin the search will bring into question the actual relationship of the evidence to the crime. Information Obtained by Microscopic F DISTRIBUT FIGURE 4-16 Hairs can be collected using tape or a special vacuum. analysis. This study has led police and the courts to regard microscopic hair comparisons as subjective; thus positive microscopic hair examinations must be confirmed by DNA analysis before they & will Bartlett be accepted as evidence in court. Microscopic F examination of hair is, however, a fast and reliable technique for excluding questioned hairs from further scrutiny. Collecting Hair Evidence Comparison of Hair A microscopic examination of the hair sample may enable the examiner to determine the area of the body from which the hair originated. Scalp hairs, for example, tend F to have a consistent diameter and a relatively uniform distribution of pigment; in some cases, they may also be dyed, bleached, or damaged. By contrast, beard hairs may be relatively coarse due to constant trimming and tend to have blunt tips from cutting or shaving; an examination of F a cross section of such a hair may reveal that it is triangular in nature. Pubic hairs, by comparison, have widely variable cross-sections and shaft diameters; these short, curly hairs also may feature continuous medullae. Hair evidence should be collected F by hand, using a Microscopic examination cannot F reveal the age DISTRIBUT bright light to illuminate the area being searched. or sex of the individual who was the source of a particular hair. The exception is infant hair; it tends to Hair evidence can be collected using a wide, transparent sticky tape, lint roller, or a special evidence be short, with fine pigment granules. Sometimes, vacuum cleaner ( FIGURE 4-16 ). Strands of hair found microscopic analysis may be able to suggest the as evidence should be individually packaged in paper packets. F If the hairs have been collected on tape, the entire lint roller or sticky tape should be packaged, complete with attached hair evidence, in a polyethylene storage bag. Control (reference) samples should be col- lected from the victim, the suspect, and any other individual who could have left hair evidence of his or her presence at the crime scene. Reference hairs should be taken from all pertinent regions Courtesy of Sirchie Fingerprint Laboratories. race of the hair s Jones owner. TABLE 4-1 lists the characteristics of human F hair that are associated with particular racial groups. Head hairs are usually the best samples for determining race, although hairs from other body areas can prove useful as well. Racial determination from the microscopic exami- nation of head hairs from infants can be difficult, however, given the rudimentary nature of hair in young children. Hairs from individuals of mixed racial ancestry may possess microscopic characteristics attributed to more than one racial group. of the body. Fifty head hairs, taken from different regions of the head, should Jones be & plucked Bartlett (hair with DNA studies have shown that many people have LL roots is to be preferred) or F cut close to the root. In DNA from multiple racial groups; F thus race cannot DISTRIBUT sexual assault cases, 24 pubic hairs also should be be divided into clearly defined categories, as many plucked or cut close to the root. people falsely believe. The identification of race is TABLE 4-1 Characteristics of Human Hair Race Diameter Cross Section Pigmentation Cuticle Undulation Negroid µm Flat Dense and clumped Prevalent Caucasian µm Oval Evenly distributed Medium Uncommon Mongolian µm Round Dense auburn Thick Never.. Forensic Applications of Microscopy: Hair 97

17 most useful as an investigative tool, but it also can An investigator must, therefore, be extremely careful to secure all fiber evidence so it will not be be an associative tool when an individual s hairs F exhibit unusual racial characteristics. F accidentally lost and make certain to avoid any cross-contamination. Most fiber evidence allows the examiner only Forensic Applications of to place it within a class. Not until a suspect has Microscopy: Fibers been identified and reference fibers & collected Bartlett from LL this individual will fiber evidence F be individualized. The forensic examiner should begin the DISTRIBUT The term fiber is used to designate any long, thin, solid object. In scientific terms, a fiber is said to examination of fiber evidence with a low-power have a high aspect ratio; that is, the ratio of its stereoscopic microscope. This technique allows length to its cross-section diameter is large. Fibers the specific fibers in question to be selected and of forensic Jones interest are classified based on their origin and F composition ( FIGURE 4-17 ). Most fibers of isolated for more detailed analysis. forensic interest are very common and are encountered daily in homes and workplaces. Natural Fibers Investigators do not have to worry about the Items of clothing, remnants of cloth, thread or composition of fibers being altered over time yarn, and pieces of rope are all commonly found because the vast majority of fibers do not undergo at crime scenes, and many are made from natural fibers. Natural fibers, which are derived from physical, biological, or chemical degradation while at a crime scene. If one part of the fiber in question plant or animal sources, include materials such as has been damaged, microscopic measurements can cotton, flax, silk, wool, and kapok. In most textile usually be taken at many other points along the materials, the natural fibers are twisted or spun fiber. Because fibers are so & small Bartlett and light, they together to form threads or Jones yarns & that Bartlett are woven LL are easily transferred from F one object to another. or knitted into fabric. When F examined under DISTRIBUT As a consequence, they often provide evidence of magnification, a thread made from natural fibers association between a suspect and a crime scene. appears to be a collection of many small twisted Of course, if a fiber was transferred once during a hairs ( FIGURE 4-18 ). crime, it may be easily transferred a second time Cotton (a plant fiber) is the most widely used such as during the investigation of the crime scene. Fibers natural fiber. In fact, undyed white cotton is so Natural F Human-Made Animal Vegetable Mineral Organic Inorganic Hair Silk Asbestos Synthetic Polymers Natural Polymers Metal Ceramic Glass Leaf (Flax) Bast (Sisal) Seed (Cotton) FIGURE 4-17 The classification of fibers. Polyolefin Polyester Nylon Acrylic Acetate Rayon Lyocell 98 CHAPTER 4 The Microscope and Forensic Identification of Hair, Fibers, and Paint..

18 form a thread or yarn. Whether the thread is a filament or a spun yarn can be determined simply by untwisting F the yarn. Filament yarns unravel into long strands of fibers, whereas spun yarns unravel into short lengths of fiber that can be easily pulled apart. Because yarn is made by twisting parallel fibers together, the twist direction is another factor LL that allows for comparison. Other F physical properties used to compare yarn samples include their DISTRIBUT texture, the number of twists per inch, the number of fibers making up each strand, the blend of fibers (if more than one is present), the color, and pilling characteristics (i.e., tufts of fiber sticking out of the main bundle). FIGURE 4-18 Threads made of natural fibers appear to be a The examination of threads of yarn is normally collection of many small fibers. done under a stereomicroscope using fine tweezers. The specimen is unraveled slowly and its features noted while being viewed under low power. F widely used in clothing and other fabrics that it has almost no evidentiary value. Animal fibers include hair from sheep (wool), goats (cashmere), Woven Fabrics llamas, and alpacas as well as fur from animals Woven fabrics are made by intertwining two sets such as rabbits and mink. Identification of animal of yarns that are placed at a 90 angle to each other fur follows the same procedure as the microscopic on a loom. The lengthwise strand, which is known LL examination of animal hair F described previously. as the warp, runs the length of the F fabric. The weft DISTRIBUT Yarn Yarns are Jones categorized into two primary groups: filament and spun. Filament yarns are made of a continuous length of a human-made fiber. Spun yarns are made of short lengths of fibers that are twisted or spun together so they adhere to each other to Phototake/Alamy Images strands are interlaced at right angles to the warp strands. The device used to weave fabrics is called a loom ( FIGURE 4-19 ). A loom can produce a variety of distinctive patterns, known as weave structure. The basic weave patterns, which can be seen in FIGURE 4-20, are plain, satin, basket, twill, and leno. The plain weave is the most common weave structure ( FIGURE 4-21 ); each weft yarn goes alternately BACK AT THE CRIME LAB Hair and fiber analysis provides a challenge when determine whether a hair fiber found at a crime scene questioned and known samples are similar but cannot be proved identical through & current Bartlett conventional riod of time in the region or if it belongs Jones to & someone Bartlett LL belongs to a person who has spent a significant pe- methods. A new set of methods F using stable isotopes who was merely passing through. Likewise, F clothing DISTRIBUT is currently being examined for its ability to provide quantitative comparison data even in situations either the location of plant growth or the chemical fibers will show specific isotopic ratios depending on in which today s tools provide only qualitative data process through which the artificial fibers were made. (such as hair follicles without tags). A caveat to Jones this new & set Bartlett of methods: The vari-llability of isotopic values, F even within a homogeneous Isotopic F forensics depends on the idea that the keratinized components of the body (nails and hair) population, makes specific identification nearly impossible. Like many of the tests described in this are formed from the by-products of the food and water that the person has consumed. Regional differences in book, isotopic analysis will be used more often to the isotopic composition of hair fibers can be used to exonerate suspects than to prosecute them. Forensic Applications of Microscopy: Fibers 99..