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FORENSIC SCIENCE Trace Evidence

FORENSIC SCIENCE Trace Evidence

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FORENSIC SCIENCE Trace Evidence

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  1. FORENSIC SCIENCETrace Evidence

  2. Introduction Trace Evidence--any small pieces of material, man-made or naturally occurring Most common examples: • Hair • Fiber

  3. Test Questions for Trace Evidence • What is it? • Is it man-made or natural? • What is its source? • How common is it? • Can it be identified to a single source?

  4. Hair Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime. It can provide a link between the criminal and the act. From hair one can determine: • Human or animal • Race • Origin • Manner in which hair was removed • Treated hair • Drugs ingested

  5. DNA The hair shaft contains abundant mitochondrial DNA--inherited only from our mothers. It can be typed by comparing relatives if no DNA from the body is available. Only the root contains nuclear DNA.

  6. Hair MorphologyThe Study of Structure and Form Parts of the hair • Shaft--part of the hair that sticks out of the skin • Root--lies below the epidermis • Follicle--structure from which the hair grows

  7. Hair Growth • Terminology • Anagen--hair that is growing • Catagen--hair at rest • Telogen--hair that is dying • Length--00.5 mm per day or 1 centimeter per month; approximately one half inch per month

  8. Mosaic Pectinate Imbricate Petal Diamond petal Chevron Hair Cuticle The cuticle is the outermost layer of hair which is covered with scales. Scales also always point toward the tip of the hair. These scales differ between species of animals and are names based on their appearance. Some of these scales are variations of the same and include:

  9. Scale Types Mosaic Chevron

  10. Scale Types (cont) Pectinate Imbricate

  11. Scale Types (cont) Petal Diamond Petal

  12. HUMAN SCALES In order to visualize the scales • paint fingernail polish on a slide • place a hair on the polish • lift off the hair and observe the scale imprints What pattern is seen in this slide?

  13. Hair Cortex The cortex gives the hair its shape. It has two major characteristics: • Melanin--pigment granules that give hair its color • Cortical fusi--air spaces, usually found near the root but may be found throughout the hair shaft

  14. Hair Medulla The medulla is the hair core that is not always present. The medulla comes in different types and patterns. Types: • Continuous • Intermittent or interrupted • Fragmented • Absent--not present

  15. Hair Medulla Patterns Uniserial Multiserial Vacuolated Lattice Amorphous (without a distinct pattern)

  16. HUMAN MEDULLA Human medulla may be continuous, fragmented or absent.

  17. RABBIT MEDULLA Rabbit medulla is different depending on the type (location on the rabbit) of hair. The one to the left is multiserial. The one to the right is a uniserial ladder and is found in guard hair.

  18. Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair. Medullary Index Medullary Index for human hair is generally less than 1/3. For animal hair, it is usually greater than 1/2.

  19. Color Length Diameter Distribution, shape and color intensity of pigments granules Dyed hair has color in cuticle and cortex Bleaching removes pigment and gives yellow tint Scale types Presence or absence of medulla Medullary type Medullary pattern Medullary index Hair Comparison

  20. Collection of Hair Evidence • Questioned hairs must be accompanied by an adequate number of control samples. • from victim • possible suspects • others who may have deposited hair at the scene • Control Sample • 50 full-length hairs from all areas of scalp • 24 full-length pubic hairs

  21. Hair Toxicology Advantages: • Easier to collect and store • Is externally available • Can provide information on the individual’s history of drug use. Collections must be taken from different locations on the body to get an accurate timeline.

  22. HAIR TESTINGProcedure • Collect an adequate sample, cut as closely to the scalp as possible. • Wash the hair to remove lipids, oils, cosmetics and any drugs adhering to it • Cut it into one centimeter sections • Place hair in a digesting solution • Screening test--antibodies are added to the hair that bind with the drugs. If this shows that drugs are present: • A confirmation test is done by gas chromatograph and then a mass spectrometer.

  23. Fiber Evidence NOTE: Fabric is the type of material and fibers are the “threads” that make up the fabric The use of fiber evidence in court cases is used many times to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers were the entire case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims. Although this case is unusual, fibers are generally considered of greater value as evidence than that of rootless hairs since they may contain a greater number of variables, thus showing more individual characteristics.

  24. Polymers Synthetic fibers are made of polymers which are long string of repeating chemical units. The word polymer means many (poly) units (mer). The repeating units of a polymer are called monomers. By varying the chemical structure of the monomers or by varying the way they are weaved together, polymers are created that have different properties. As a result of these differences, forensically they can be distinguished from one another.

  25. Analysis of FibrousMaterial U.S. Department of Justice FBI, April 1999

  26. Synthetic Polyester Rayon Nylon Acetate Acrylic Spandex Natural Silk Cotton Wool Mohair Cashmere Types of Fibers

  27. Classification Classified according to their origin: • Vegetable or cellulose • Animal or protein • Mineral

  28. Cellulose Fibers • Cotton--vegetable fiber. Strong, tough, flexible; moisture absorbent; not shape retentive • Ramie--vegetable fiber. Less flexible than cotton so its often blended with cotton • Rayon--first man-made fiber; soft, lustrous, versatile fiber Cellulose esters--cellulose is chemically altered to create an entirely new compound not found in nature. • Acetate--less expensive, less polluting than rayon

  29. Fiber Comparison Can you tell the difference(s) between the cotton on the left and the rayon on the right?

  30. Petroleum Plastics(Made from derivatives of petroleum, coal and natural gas) • Nylon--most durable man-made fabric; extremely light weight • Polyester--most widely used man-made fiber • Acrylic--provides warmth from a lightweight, soft and resilient fabric • Spandex--extreme elastic properties

  31. Protein Fibers • Wool--animal fiber coming most often from sheep but may be goat (mohair), rabbit (angora), camel, mink, beaver • Silk--animal fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulating properties Wool Fibers (400X)

  32. Mineral Fibers • Asbestos--a natural fiber that was used in fire-resistant substances • Metallics (mylar)--a manufactured mineral fiber • Fiberglass--another manufactured mineral fiber

  33. Fabric Production Fabrics are composed of individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness and durability are all individual qualities of the different fabrics.

  34. Woven Fabric Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage which is the edge of the fabric. Weft cross over and under the warp threads. Types include: • Plain • Twill • Satin

  35. Woven Fabric • PLAIN • Simplest and most common weave • Warp and weft pass under each other alternately • Create even patterns of 1/1 and 2/2 • Design resembles a checkerboard

  36. Woven Fabric • TWILL • Create by passing the warp yearn over one to three weft yearns before going under one • Makes a diagonal weave • Design resembles a stair steps • Denim is the most obvious example

  37. Woven Fabric • SATIN • The yarn interlacing is not uniform • Creates long floats • Interlacing weave passes over four or more yarns • Satin is the most obvious example

  38. Knitted Fabric Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.. Diagram:

  39. Identification andComparison of Fibers • Microscopic examination • Color--compositional differences in the dyes • Fibers surface--delustering particles that may be added by manufacturers • Microspectrophotometer--compares fiber colors through spectral patterns • Chromatography--gives a more detailed analysis of the dye composition

  40. Identification andComparison of Fibers (cont.) • Polarizing microscope • can be used to determine the refractive indices of various fibers. The fiber is immersed in a fluid that has a comparable refractive index. The disappearance of the Becke line is observed under the microscope. • In addition, fibers will absorb infrared light in a characteristic pattern. This can be observed through the use of an infrared microspectrophotometer and a microscope.

  41. Collection of Fiber Evidence • Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged. • Make tape lifts of exposed skin areas of bodies and any inanimate objects • Removed fibers should be folded into a small sheet of paper and stored in a paper bag

  42. Uniqueness Establishing Individual Characteristics • If there is only one source for the transfer material with a controlled environment where the contact took place • If there is contamination of several different materials from surface onto surface two • If there is a method available to characterize the material, such as applying DNA Otherwise, trace evidence would have only class characteristics.

  43. Man, I was nailed when those forensic guys found fibers from the kid’s math assignment in my teeth.