Forensics: Chapter 8

1. Forensics: Chapter 8 Hairs, Fibers & Paint

2. Objectives: • Describe techniques for describing, identifying, and differentiating samples of human and non-human hair. • Describe techniques for describing, identifying, and differentiating samples of fibers. • Describe techniques for differentiating samples of paint chips.

3. Hair, Hair, Everywhere! • It is not yet possible to individualize a human hair to any single head or body through its morphology. • However, hair does have evidentiary merit. • When collected properly and submitted to a forensic laboratory with an adequate number of standard/reference samples, hair can provide strong corroborative evidence for placing an individual at the scene of a crime.

4. Parts of a Hair: • Root or bulb (embedded in a hair follicle) • Shaft • Tip

5. Hair Shaft: • The shaft portion of the hair is subjected to the most intense examination by forensic scientists. Parts of the Shaft: • Cuticle – outside covering of hair ** • Cortex – main body of hair shaft • Medulla – center column of hair **

6. Cuticle: • The cuticle is primarily responsible for two features that make hair a good subject for establishing identity of an individual: 1. chemical decomposition (most resistant) 2. ability to retain structural features • The cuticle is formed by overlapping hardened (keratinized) scales that always point toward the tip of the hair.

7. Good to Know: • The scales of animals have a variety of patterns that make them helpful in distinguishing among species of animals. (see Figure 8-2) • Shaft length of hair is MOST important for making species comparisons. • A cast of a hair surface can be made by using a soft medium such as softened vinyl or clear nail polish.

8. Cortex: • The cortex is the main body of the hair shaft. • The cortex is contained within the protective layer of the cuticle. • The cortex is embedded with pigment granules that impart hair with color. Color, shape, and distribution of these granules provide a criminalist with important information that allows them to compare against the hairs of different individuals.

9. Medulla: • The medulla is a cellular column (central canal) running through the center of the hair. • The medulla is the dominant feature comprising more than half of the hair’s diameter. • The medullary index measures the diameter of the medulla relative to the diameter of the hair shaft and is normally expressed as a fraction. • Medullary indices for humans generally have a value of less than one-third or may be absent entirely; for most other animals, the value is one-half or greater.

10. Medulla (cont): • The presence and appearance of the medulla vary between individuals and among the hairs of a given individual (two hairs from the same head may not have the same morphological characteristics). • Medullae can be classified as continuous, interrupted, fragmented, or absent (see Fig 8-3)

11. Medulla (cont) • Medullae can be classified as continuous, interrupted, fragmented, or absent (see Fig 8-3) • Humans – generally have no medullae or have fragmented one (exc: Mongoloid race which are continuous) - medullae is nearly cylindrical in appearance • Animals – generally exhibit medullae that are either continuous or interrupted. • Medullae can be vary in shape ex: cat: string of pearls ex: deer: spherical cells along entire hair shaft

12. Root: • Human head hair grows in 3 developmental stages. • Rate of human hair growth per month is 1 cm. • The shape and size of the hair root is determined by the growth phase in which the hair happens to be.

13. 3 Developmental Hair Stages: • Anagen • Catagen • Telogen

14. Anagen Phase: • Initial growth phase during which the hair follicle is actively producing hair. • May last up to six years • Root is attached to the follicle giving the root bulb a flame-shaped appearance • When pulled from the root, anagen hairs will contain a follicular tag (translucent piece of tissue surrounding the hair’s shaft near the root. It contains the richest source of DNA associated with hair).

15. Catagen Phase: • Transition stage • Hairs continue to grow but at a decreasing rate • May last from two to three weeks • Roots typically have an elongated appearance (root bulb shrinks and is being pushed out of the hair follicle).

16. Telogen Phase: • Final growth phase in which hair naturally falls out of the skin • Root takes a club-shaped appearance • During a 2 to 6 month period, the hair will be pushed out of the follicle causing hair to be naturally lost.

17. Identification and Comparison of Hair: • Usually when hair evidence is present in a criminal case, the primary purpose for its examination is to determine if the hair is human or animal in origin (generally not very difficult to ascertain) or whether human hair retrieved at a crime scene compares with hair known to have come from a particular individual.

18. Forensic Hair Considerations: When comparing hair, the criminalist is particularly interested in matching the following: • color • length • diameter • presence or absence of medulla • distribution, shape, and color intensity of the pigment granules in the cortex • morphological abnormalities (due to certain diseases or deficiencies) • presence of fungal and nit infections

19. Can The Body Area From Which A Hair Originated Be Determined? • Scalp Hair – little diameter variation and more uniform distribution of pigment color as compared to other body hairs. • Pubic Hair – wide variations in shaft diameter and usually have continuous medullae • Beard Hair – normally triangular in cross section with blunt tips due to shaving

20. Can the Racial Origin of Hair Be Determined? • All observations are general with many possible exceptions. • Africoid – hair is kinky, - contains dense, unevenly distributed pigments - cross section of hair is flat to oval in shape. • Caucasian – usually straight or wavy - fine to coarse pigments that are more evenlydistributed than Africoid hair. - cross section of hair is oval to round in shape

21. Can the Age and Sex of an Individual Be Determined from a Hair Sample? • Age – cannot be determined with any degree of certainty (except with infant hair) • Sex – recovery of nuclear DNA from either tissue adhering to the hair or from the root structure will allow for sex determination.

22. Is It Possible to Determine If Hair Was Forcibly Removed from the Body? • Hair root with follicular tissue (root sheath cells) attached to it is indicative of hair that has been pulled out either by another person or by brushing or combing. The rate at which hair was removed does affect the tissue adherence.

23. Are Efforts Being Made To Individualize Human Hair? • Hair can be linked to a particular individual by characterizing the nuclear DNA present in the hair root or in the follicular tag (best in anagen phase). • If nuclear DNA identification is not possible, the criminalists can employ mitochondrial DNA analysis (usually highly successful if hair length is in the range of at least 1 to 2 cm). • Mitochondrial DNA – DNA found outside the nucleus in mitochondria. Maternally inherited.

24. Can DNA Individualize A Human Hair? • Not technically. • But, it can help exclude a significant portion of a population as potential contributors of a hair sample.

25. Collection And Preservation Of Hair Evidence: • Collected evidence samples must be submitted to forensic laboratory for examination accompanied by an adequate number of standard/reference samples from the victim of the crime as well as the suspects. • Victim: This is usually done during the autopsy. • Suspects: May require a court order.

26. Famous “Hair” Cases: • Central Park Jogger • Ennis Cosby • See pgs 201 & 204

27. Types of Fibers: • Fibers may become important evidence in incidents that involve personal contact. • Ex: homicide, breaking and entering, assault, hit and run, sexual assault • Great care should be taken in the collection of fiber evidence to avoid cross-contamination of evidence.

28. Fiber Categories: • Fibers are classified into 2 broad categories: • Natural • Man-made

29. Natural Fibers: • Fibers derived entirely from animal or plant sources. • Examples include hair coverings from sheep (wool), goats (mohair, cashmere), camels, llamas, alpacas, mink, rabbit, beaver, and muskrat. • The most prevalent plant fiber is cotton. • Cotton fiber shows a microscopic ribbon like shape with twists at irregular intervals.

30. Man-Made (Synthetic) Fibers: • Fibers derived from either natural or synthetic polymers • These fibers are typically made by forcing the polymeric material through the holes of a spinneret. • The first man-made fiber was rayon (regenerated fiber made from natural raw materials) • Synthetic fibers – nylon, polyester, and acrylic

31. Polymers: • Polymer – basic chemical substance of all synthetic fibers. • Substances made from polymers include plastics, paints, adhesives, and synthetic rubber • Starch and cellulose are natural carbohydrate polymers

32. Fibers: When comparing two fibers, the following properties should be examined: • Color • Diameter • Birefringence • Presence or absence of delustering particles

33. Jig Saw Evidence: • It is a virtual certainty that two fabrics share a common origin if their fibers can be fitted together at their torn edges.

34. Forensic Examination of Paint: • Paint – most frequently encountered physical evidence in hit and run and burglary cases.

35. Paint Composition: Consists of: • A binder • A solvent • Pigments

36. Paint: • The polymeric make-up of paint binders can readily be compared by pyrolysis gas chromatography and IR spectrophotometry.

37. Paint: • Paint chips may be individualized to a single source by examining their color and layer structure. • The color-layer sequence imparts paint with its most distinctive forensic characteristics.

38. 4 Coatings of Auto Finishing: • The automobile finishing system for steel usually consists of at least 4 organic coatings: 1. Electrocoat Primer – first layer applied to the steel body provides corrosion resistance - color ranges from black to gray 2. Primer Surfacer – used to completely smooth out and hide any seams or imperfections - highly pigmented layer 3. Basecoat – layer used to provide color and aesthetics of the finish (“eye-appeal”) 4. Clearcoat – unpigmented layer used to improve gloss, durability and appearance. - helps resist UV radiation and acid rain

39. Paint Data Query: • The PDQ allows an analyst to obtain information on paints related to the following: • automobile make • model • year