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Trace Evidence, Hair, and Fibers

Trace Evidence, Hair, and Fibers

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Trace Evidence, Hair, and Fibers

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  1. Trace Evidence, Hair, and Fibers Coach Whitaker

  2. Vocabulary • Trace evidence—is any small physical material that can be transferred from person to person or a crime scene • Follicle—tubelike organ on the body that hair grows from • Cuticle—is the clear outside covering of the hair shaft • Cortex—contains the pigment of hair strand and provides strength to the hair

  3. Vocabulary • Medulla—interior core of the hair and provides it flexibility • Fibers—are any threadlike element of a material • Textile—a fabric woven in a distinctive pattern • Fabric—a cloth material made up of fibers woven or bonded in a certain manner

  4. Trace Evidence • Trace evidence is physical evidence found in small amounts at a crime scene • Common examples are hair, fibers, paint chips, body fluids, stains, powders, explosive residue, glass particles, metals, and soil • Trace evidence is any small material that can be transferred from person to person or a person and crime scene

  5. Trace Evidence • Criminals are clever or they think they are • Trace evidence creates links between suspects, places, and objects • Trace evidence is often the only evidence that connects a person to a crime scene

  6. Trace Evidence • An extremely important characteristic of trace evidence is its transferability • It grabs and clings to clothing, hides in shoe seams, nestles in hair, and settles in nooks and crannies • It survives for months or years

  7. Trace Evidence • The analysis of trace evidence requires a thorough investigation of its physical and chemical properties • Because most trace evidence is very small, it cannot be adequately examined with the naked eye

  8. Trace Evidence • Equipment used to analyze TE • Comparison Microscope—provides a side by side comparison • Mircospectrophotometry—the exact color of an object can be measured • Polarized light microscope—helps objects appear more sharp and the colors are clearer • Scanning Electron Microscope—magnifies an objects up to 100,000 times the original size • Stereomicroscope—helps provide a FS a 3-D model of an object

  9. Equipment photos Comparison Microscope Mircospectrophotometry Polarized light microscope Stereomicroscope Scanning Electron Microscope

  10. Activity • Trace Evidence Collage • Think of at least 15 pieces of trace evidence

  11. Hair • Investigators often find hair at crime scenes • Hair is considered class evidence and is useful in backing up circumstantial evidence (ex. Places someone at a scene)

  12. Hair • The average human body has 5 million hairs • Blond hair people have the most hair on their hand (120,000 strands) followed by Black and brown (100,000 strands) and Redheads (80,000 strands) • Hair is continuously shed and renewed at a rate of 100 each 24 hour period from the scrape alone

  13. Hair • Hair is made up of complex-cross protein polymers that are resistant to breaking down • It grows from a tubelike organ in the under layer of the skin called a hair follicle • The root is embedded in the follicle and linked to the body’s blood supply

  14. Biology of Hair Hair is composed of the protein keratin, which is also the primary component of finger and toe nails. Hair is produced from a structure called the hair follicle. Humans develophair follicles during fetal development, and no new follicles are produced after birth. Hair color is mostly the result of pigments, which are chemical compounds that reflect certain wavelengths of visible light. Hair shape (round or oval) and texture (curly or straight) is influenced heavily by genes. The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.). The body area (head, arm, leg, back, etc.) from which a hair originated can be determined by the sample’s length, shape, size, color, and other physical characteristics. In order to test hair evidence for DNA, the root must be present. Sources: &

  15. Hair Structure Medulla – central core(may be absent) Cortex – protein-rich structure around the medulla that contains pigment Hair is composed of three principal parts: Cuticle – outer coating composed of overlapping scales The structure of hair has been compared to that of a pencil with the medulla being the lead, the cortex being the wood and the cuticle being the paint on the outside.

  16. Hair Structure • Cuticle • The cuticle varies in: • Its scales, • How many there are per centimeter, • How much they overlap, • Their overall shape, and • How much they protrude from the surface • Its thickness, and • Whether or not it contains pigment. Characteristics of the cuticle may be important in distinguishing between hairs of different species but are often not useful in distinguishing between different people.

  17. Hair Structure • Cortex • The cortex varies in: • Thickness • Texture • Color • Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come. • Microscopic examination can also reveal the condition and shape of the root and tip. Info: Image:

  18. Hair Structure Like the cuticle, the medulla can be important for distinguishing between hairs of different species, but often does not lend much important information to the differentiation between hairs from different people. • Medulla • The medulla may vary in: • Thickness • Continuity - one continuous structure or broken into pieces • Opacity - how much light is able to pass through it • It may also be absent in some species.

  19. Hair At The Crime Scene • 1st the investigator must determine if the hair is animal or humans (root bulb-like or spear shape) • Characteristics are studied • Each person with hair have hairs with different characteristics and may have similarities • Hairs strains may be different from the same person • Things we learn from hair: whether the source is animal or humans, racial origins (sometimes), location on the source’s body

  20. Activity • Hair Lab •

  21. Fibers • Fibers are any threadlike element of a material and are everywhere • Because textiles are massed produced, it is difficult to trace it back to a specific source but it could create a link between victims, suspects, and places • Statistics and probability play a big role • Like hair, textile fibers are common items left at a crime scene

  22. Natural Fibers Many different natural fibers that come from plants and animals are used in the production of fabric. Cotton fibers are the plant fibers most commonly used in textile materials The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.

  23. Fibers under a microscope Synthetic Fibers More than half of all fibers used in the production of textile materials are synthetic or man-made. Nylon, rayon, and polyester are all examples of synthetic fibers. Cross-section of a man-made fiber Images:

  24. Fibers • Fabrics are made from fibers • Fibers are used to make textiles, such as cloth or carpeting; rope, string, brushes, and filling materials

  25. Fibers • Time is critical when collecting fibers because studies show fibers clinging to clothing are lost quickly • After four hours, 80% of fibers have fallen away and after 24 hours, 95% may be gone • Fibers can be lifted from clothing from tape or vaccuming • At the crime scene, fibers can be found focal point of the crime

  26. Fibers • Comparing fibers • FS access fibers by assessing their diameters, shapes, colors, shininess, and curls and crimps, and then looking for any attached debris

  27. Activity • Hair and Fiber ID •

  28. Class Project • Classroom Crime Lab • Hair and Class Crime