Hairs, Fibers, and Paint

1. Hairs, Fibers, and Paint Chapter 13

2. Hair • Hair morphology (structure) is a class characteristic, not an individual characteristic • Hair evidence can indicate physical/violent contact • Retains structure for a long time • Analyze color & structure first • DNA typing can be used later for identification • if follicle cells are found • if mitochondrial DNA is used • Basic Morphology • Root bulb in hair follicle • Long shaft with 3 layers: cuticle, cortex, and medulla • Tip end

3. Hair Morphology—Cuticle & Cortex • Cuticle • Protective outer layer on hair • Mostly keratin protein • Scale pattern distinguishes different animal hairs • Scales are composed of hardened dead cells • Cortex • main body of hair shaft • spindle-shaped cortical cells • contains pigment granules that give hair color • compare color, shape, and distribution of granules

4. Hair morphology—Medulla • Medulla • Cells down the center of hair • Look like central canal • Can be continuous, interrupted, fragmented, or absent • Identify hair type and species by pattern • Medullary index • Calculate ratio of diameter of medulla to diameter of hair • Distinguish human hairs (index < 1/3) from animal hairs

5. Hair growth in the root • Anagen phase • Initial growth phase where the hair follicle produces hair • May take up to 6 years • Catagen phase • 2-3 week transition stage • Growth slows, root shrinks • Telogen phase • Hair has stopped growing and slowly falls out naturally • May take 2-6 months • Pulled hairs (anagen phase) have follicular tag which contains DNA for analysis

6. Distinguishing Human and Animal Hair • Be aware of morphological differences • within individuals/species • between individuals/species • Compare to reference samples using a microscope • Check: • Cuticle scale structure • Medullary index (<1/3) • Medulla pattern or shape

7. Matching human hair from crime scene • Head or pubic hair recovered from crime scene must be matched to reference sample taken from individual • Comparison microscope: match color, length, diameter, medulla pattern, color intensity and pigment distribution in cortex • Fungal, bacterial, or insect infections can cause unusual features • Not foolproof – 11% false positive rate!

8. Identifying types of hair • Variations in color, texture and patterns within types of hair for one individual • Scalp hairs: uniform diameter, uniform pigment distribution • Pubic hairs: short, curly, continuous medullae, wide diameter variations • Beard hairs: coarse, triangular, blunt tips from shaving

9. Racial Identity from Hair • Negroid Hair • Usually coarse and tightly curled • Flat to oval cross-section • Dense, unevenly distributed pigment • Caucasian Hair • straight or wavy • fine to coarse • pigments are more evenly distributed • Circular to oval cross-section

10. Determining Age and Gender from hair • Infant hairs are fine and short with fine pigmentation • Nothing else about age can be determined from hair • Presence of dye/bleach might help determine gender • Analysis of DNA from hair follicle can be used for gender analysis

11. Definite Identity • Hair alone cannot be used for definitive identity without DNA analysis of follicle cells • Central Park Jogger case (1989-2002) • http://www.youtube.com/watch?v=fGc4PaLB-ek

12. Hair collection and preservation • Get many standard reference samples from victims and suspects from various body locations • Can be a lot of variation in any one region; so many reference hairs from that area are necessary • Usually 50 scalp hairs and 24 pubic hairs are collected for comparison

13. Fiber Analysis • Fibers from fabric or garments are collected from crime scene • Crimes with physical contact • Assaults, homicides, sex crimes • Hit-and-run • Breaking and entering • Identify type and source • Compare to reference samples collected from suspects’ belongings

14. Natural Fibers • Wholly derived from animal or plant sources • Most common is animal hair • wool, furs, mohair, cashmere, etc. • Perform hair analysis with microscope • Cotton is the most prevalent plant fiber • Analyze microscopically for color and morphological characteristics

15. Manufactured Fibers • Garment fibers derived from natural or synthetic polymers like nylon and rayon • Regenerated fibers • Raw material is natural: cotton or wood pulp • Cellulose is extracted and chemically treated or dissolved • Forced through small holes of a spinning jet • Include rayon, acetate, triacetate • Synthetic fibers • made from synthetic chemicals • Include nylon, polyester, spandex, and acrylic • Polymer • Very long, repeating macromolecule • Synthetic polymers (polyester, etc) • Natural polymers such as cellulose, starch, and keratin

17. Identifying Manufactured Fibers • First step: microscopic analysis for color, diameter, shape, and patterns • If they match, do further analysis • Dye composition • Visible-light microspectrophotometer • Mount fibers on microscope slide • Uses spectral patterns to compare fiber colors • Works even with a tiny sample • Chromatograph separation • Extract dyes from fiber • Put spot of dye on thin-layer chromatography plate • Colors separate and can be compared

18. Chemical Composition of Fibers • Fibers that match morphological and color characteristics are compared to see if same chemicals are present • Verifies that a set of fibers come from same class: Which type of nylon or acrylic? • Works on very small sample

19. Birefringence • Crystalline manufactured fibers cause double refraction • A beam of light shifts when it travels through the material • Different materials have different indexes of refraction • Immerse fiber in similar liquid and see it disappear • Shine polarized light through fiber, measure birefringence • Does not harm fiber

20. Infrared Absorption • Different manufactured polymers absorb infrared light in different characteristic patterns • Done with spectrophotometer connected to microscope = microspectrophotometer • Identify the generic class (nylon, acrylic, etc) and sometimes more specific type

21. Fiber Evidence Significance • Can be used to determine group characteristics that can be matched to reference samples • Factories produce lots of identical clothing with identical fibers • More powerful if two or more fibers match • Can be used as supporting evidence • Not strong individual evidence • Fiber video: • youtube.com/watch?v-BjLHW7qQEIO

22. Paint Analysis • Electrocoat Primer—first layer of auto paint; electroplated primer for corrosion resistance; black to gray • Primer Surfacer—On top of electrocoat; corrosion resistance; hides any seams or imperfections • Basecoat—colorcoat provides color and finish; resists weather, UV radiation; metals are added to add luster to paint • Clearcoat—unpigmented to improve gloss, durability and appearance

23. Microscopic Analysis of Paint • Color and appearance of evidence chips are compared to known samples under a microscope • Most important and most common analysis tool for paint

24. Chemical Analysis of Paint • Pyrolysis Gas Chromatography is used to separate and to isolate the chemical components of paint • Since paint components cannot be dissolved into a solvent for gas chromatography. • So, paint samples are heated very high (pyrolyzed) so that they decompose into gaseous products that can be separated via chromatography. • Paint pyrograms show chemical make up of binder

25. Spectroscopy • Line spectrum of each element is different • Can be used to identify elements in a paint sample • Plasma Emission Spectrometry is replacing other traditional means; uses a hot plasma torch to see response to light energy

26. Paint Data Query • Paint database for automobile paint comparisons • Can match evidence samples to year and make of car • Then, only need reference samples from that year and model