Presentation is loading. Please wait.

Presentation is loading. Please wait.

Trace Evidence, Hair, and Fibers Coach Whitaker. Vocabulary Trace evidence—is any small physical material that can be transferred from person to person.

Similar presentations


Presentation on theme: "Trace Evidence, Hair, and Fibers Coach Whitaker. Vocabulary Trace evidence—is any small physical material that can be transferred from person to person."— Presentation transcript:

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 1. Comparison Microscope—provides a side by side comparison 2. Mircospectrophotometry—the exact color of an object can be measured 3. Polarized light microscope—helps objects appear more sharp and the colors are clearer 4. Scanning Electron Microscope—magnifies an objects up to 100,000 times the original size 5. Stereomicroscope—helps provide a FS a 3-D model of an object

9 Equipment photos Comparison Microscope MircospectrophotometryPolarized light microscope Scanning Electron Microscope Stereomicroscope

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 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.). Sources: & 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 develop hair 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. 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. Biology of Hair In order to test hair evidence for DNA, the root must be present.

15 Hair Structure Hair is composed of three principal parts: 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. Cuticle – outer coating composed of overlapping scales Cortex – protein-rich structure around the medulla that contains pigment Medulla – central core (may be absent)

16 Characteristics of the cuticle may be important in distinguishing between hairs of different species but are often not useful in distinguishing between different people. 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.

17 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: Hair Structure

18 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. 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. Hair Structure

19 Hair At The Crime Scene 1 st 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 ml#hairsfibers ml#hairsfibers

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 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. Natural Fibers

23 Images: 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 Synthetic Fibers Fibers under a microscope

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 hairfiber_IDlabwkst.pdf hairfiber_IDlabwkst.pdf

28 Class Project Classroom Crime Lab Hair and Class Crime


Download ppt "Trace Evidence, Hair, and Fibers Coach Whitaker. Vocabulary Trace evidence—is any small physical material that can be transferred from person to person."

Similar presentations


Ads by Google