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Lecture on Trace Evidence.ppt
- 2. 2 Introduction Trace Evidence--any small or microscopic pieces of material, man-made or naturally occurring which relates to the commission of a crime and can help to place a suspect at the scene of crime. Most common examples: Hair Fiber
- 3. 3 Hair Human hair is one of the most frequently found pieces of trace 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
- 4. 4 Hair - Racial Identification Mongo loid or Asianha ir Negroid or African hair Caucasian or European hair
- 5. How does scalp hair vary by race? Asian/Native American/Mongoloid Hairs – Round hair shaft - straight – Large pigment granules – Patchy distribution of pigment – Usually continuous medulla European/Caucasian – Slightly round to oval hair shaft (straight to curly) – Finer pigment granules – More even distribution of pigment – Usually absent or fragmented medulla
- 6. How does scalp hair vary by race? African American/Negroid – Flat to oval hair shaft (curly to kinky) - Largest and most dense pigment granules that are unevenly distributed -Absent or fragmented medulla
- 7. 7 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.
- 8. 8 Hair Morphology The 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
- 9. 9 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
- 10. 10 Three major parts of Hair shaft: –Cuticle –Cortex –Medulla
- 11. Hair Morphology – Cross Section
- 12. 12 Cross Section of Hair The hair shaft is comprised of 3 different layers: Cuticle: • Outer layer, which protects the hair. Cortex: •Middle layer •Main body of shaft, contains pigment granules Medulla: •Central core of the hair. •Composed of soft keratin.
- 13. 13 Hair Cuticle Mosaic Pectinate Imbricate Petal Diamond petal Chevron 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 named based on their appearance. Some of these scales are variations of the same and include:
- 15. 15 Scale Types (cont) Pectinate Imbricate
- 16. 16 Scale Types (cont) Petal Diamond Petal
- 17. 17 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
- 18. 18 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
- 19. 19 Cont.. • Contains pigment granules •Compare color, shape, distribution • Made up of long thin cells firmly attached to each other and arranged lengthwise • Provides hair with strength, elasticity and determines the texture and quality of hair
- 20. 20 3) Medulla • Cellular column running through middle of hair • Shape - human and most animals have cylindrical shape • Vary from person to person AND among hairs from one person • Best used to distinguish if a sample is human or animal. (medulla index) Human takes up <1/3 hair shaft Other animals takes up >1/2 hair shaft
- 21. 21 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 Hair Medulla
- 22. 22 Hair Medulla Patterns Uniserial Multiserial Vacuolated Lattice Amorphous (without a distinct pattern)
- 23. 23 HUMAN MEDULLA Human medulla may be continuous, fragmented or absent.
- 24. 24 Medullary Index Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair. Medullary Index for human hair is generally less than 1/3. For animal hair, it is usually greater than 1/2.
- 25. Medullary Index Measure of the diameter of the medulla relative to the diameter of the hair shaft Usually expressed as a fraction – Humans: medullary index < 1/3 – Animals: medullary index > 1/2
- 26. 26 Hair Comparison 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
- 27. 27 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
- 28. How is hair analyzed? Two ways: Visual Observation- simplest method of identification done with the naked eye, indicate color, length, and amount of curl. Microscopic Examination-Reveals characteristics of its physical structure.
- 29. 29 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.
- 30. 30 HAIR TESTING Procedure 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.
- 31. Substance Urine Hair Blood/Saliva Alcohol 6–24 hours up to 2 days 12–24 hours Methamphetami ne 3 to 5 days up to 90 days 1–3 days MDMA (Ecstasy 24 hours up to 90 days 25 hours Cannabis 3 to 7 days, up to >30 days after heavy use and/or in users with high body fat up to 90 days 2–3 days in blood, up to 2 weeks in blood of heavy users. Saliva for 2–6 hours Cocaine 2 to 5 days up to 90 days 2 to 5 days Cotinine (a break-down product of nicotine) 2 to 4 days up to 90 days 2 to 4 days
- 32. Forensic Analysis of the Hairs Somatic regions can be determined based on the hair’s morphology, such as: – Head hairs have a soft texture, cut or split tips, and moderate shaft diameter. – Pubic hairs have a course, wiry texture, tapered, rounded, or abraded tips, and a buckling shaft. – Facial hairs have a triangular cross- section and a course in texture. – Eyelash/Eyebrow hairs are saber- like in appearance, short, and stubby. – Limb hairs are soft, and arc-like in appearance. Tips are rounded and abraded; scales rounded due to wear. Head Hair Beard Hair Pubic Hair
- 33. Cont,, Using a microscope (SEM), forensic scientists can typically determine the species, race, and somatic origin of a hair. They may use comparative microscopy to do one of the following: – Link the suspect to a crime scene, meaning that a control hair matches the evidential hair. – Exclude the suspect from a crime scene, meaning that a control hair does not match the evidential hair. In addition to comparing hairs in with a microscope, the scientists may test for DNA on the follicular tag, and run a number of tests for drugs and environmental toxins, which will be Scanning Electron Microscope, a typical device used to study the structures of hair.
- 34. Cont,, Hair analysis is used in forensic toxicology to test and determine whether a drug was used. When a drug is ingested, it enters the blood stream and is broken down to a specific metabolite. Hair strands normally grow at an average rate of 1.3 centimeters every month; they absorb metabolized drugs that are fed to the hair follicle through the blood stream. The drug will only disappear if exposure to the drug is ceased, and the hair containing the drug is cut. Hair analysis can be used for the detection of many therapeutic drugs and recreational drugs, including cocaine, heroin, benzodiazepines (Valium-type drugs) and amphetamines. Depicting how drugs enter the hair. General structure for amphetamines. Cocaine’s Structure
- 35. Cont,, The radioimmunoassay and enzyme-linked immunosorbent assay are two common assays that are used by forensic toxicologists to detect substances such as drugs in the hair. Recall that the immunoassays function on the basis of an antigen-antibody interaction. The analyte, or drug, is added and binds to the solid phase, typically producing a color change, fluorescence, etc. that can be measured to determine the amount of drug present. Forensic toxicologists also look for toxic metals in the hair to explain poor mental and physical health. How an ELISA functions
- 36. Cont,, Individualization has been impossible to obtain with hairs in the past, but recent techniques are making it more realistic. Nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) can be extracted from the root or follicular tag of an anagenic hair. Nuclear DNA comes from both parents; mitochondrial DNA is passed only from mother to offspring. Nuclear DNA can lead to individualization. DNA Smear of anagenic hair
- 37. 37 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.
- 38. 38 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.
- 39. 39 Types of Fibers Synthetic Polyester Rayon Nylon Acetate Acrylic Spandex Natural Silk Cotton Wool Mohair Cashmere
- 40. 40 Classification Classified according to their origin: Vegetable or cellulose Animal or protein Mineral
- 41. 41 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
- 42. 42 Cont,, 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
- 43. 43 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)
- 44. 44 Mineral Fibers Asbestos--a natural fiber that was used in fire-resistant substances Metallics (mylar)--a manufactured mineral fiber Fiberglass--another manufactured mineral fiber
- 45. 45 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.
- 46. 46 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
- 47. 47 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
- 48. 48 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
- 49. 49 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
- 50. 50 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:
- 51. 51 Identification and Comparison 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
- 52. 52 Identification and Comparison 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.
- 53. 53 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
- 54. 54 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.
- 55. Man, I was nailed when those forensic guys found fibers from the kid’s math assignment in my teeth.