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Trace Evidence Part II

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  1. Trace EvidencePart II

  2. Summary • Microscopic Analysis • Types of Trace Evidence • Glass • Hair (fur) • Fibers • Paint • Soil • Gunshot Residue

  3. Hair • What is hair? • What crimes are hair involved in? • How is hair collected? • How is hair analyzed in the lab?

  4. Trace > Hair What is hair? • Natural fibers of animal origin • Terms: human = hair; animal = fur • Usually growing (live root)

  5. Trace > Hair What is hair? • Cellular material in the hair shaft (mtDNA) • Good DNA in the hair root for forcibly removed hairs (STR)

  6. Trace > Hair What crimes are hairs involved in? • Hairs are shed from people; can link a person to a crime scene. • Animal fur may also link a person to a crime scene.

  7. Trace > Hair How is hair collected? • Visually by hand or with forceps. • Possibly tape lift. • Packaged in sealed containers.

  8. Trace > Hair How is hair analyzed? Look at class characteristics (microscope): • Color • Medulla, Cortex, Cuticle

  9. Trace > Hair How is hair analyzed? Medulla: • Line down middle of hair • Species ID or human ID • Present, absent, or fragmented

  10. Trace > Hair How is hair analyzed? Cortex: • Color of hair • Species ID or human ID • May contain pigment blotches • May contain air pockets

  11. Trace > Hair How is hair analyzed? Cortex: • Humans = 1 color entire length • Animals = color can vary at root/middle/tip

  12. Trace > Hair How is hair analyzed? Cuticle: • “Scales” on outside of hair • Species ID only • Humans = imbricate

  13. Trace > Hair How is hair analyzed? (cuticle) Procedure: • Put clear nail polish on slide. • Place hair in nail polish; wait to harden. • Remove hair; look at indentations in nail polish (microscope).

  14. Fibers Fibers are very useful as trace evidence: • Vary widely in class characteristics color, shape, chemical composition, etc. • Easily transferred from one source to another (carpets, clothes, etc.) • Significant persistence (won’t degrade)

  15. Trace > Fibers How are fibers used as evidence? • As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.

  16. Trace > Fibers How long do fibers persist? Most fiber evidence is lost (fall off) a short time after the transfer occurs. The fibers that do remain will be persistent.

  17. Trace > Fibers Fibers can be classified into three main categories: • Natural (animal, plant, mineral) • Manufactured • Synthetic

  18. Trace > Fibers > Natural Natural Fibers: • Found in nature • Can be artificially colored or treated Cotton Wool Hemp

  19. Trace > Fibers > Natural Animal Fibers Wool - Hairs from sheep • Most common of animal fibers • Hairs are spun to form thread Silk - comes from silkworm • Spun as double filament (separated before use) • Because of length, doesn’t shed easily Other Hairs from Animals

  20. Trace > Fibers > Natural Plant Fibers Cotton - seed hairs of cotton plant • by far most common fiber(find almost everywhere) Under microscope, fibers resemble twisted ribbon

  21. Trace > Fibers > Natural Other Plant Fibers: Linen - stem fiber from flax plant Kapok - from seed hairs of kapok plant Other fibers - Manila, hemp, sisal, jute

  22. Trace > Fibers > Natural Mineral Fibers Asbestos - crystalline material • Used to be used for insulation • Fractures into thin rods that can get into your lungs; can kill you • Not used much anymore

  23. Trace > Fibers Filament vs. Staple Filament: Long continuous fiber (like silk) Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton)

  24. Trace > Fibers > Manufactured Manufactured Fibers Regenerated Fibers • Cellulose is dissolved, then resolidified to form the polymer fiber • Can occur in filament or staple form Example:Rayon

  25. Trace > Fibers > Synthetic Synthetic Fibers • Man made • Can also be filament or staple Examples: Nylon and Polyester

  26. Trace > Fibers > Synthetic Synthetic Fibers Acrylics • More common as evidence • Usually in staple form • Staples spun together, similar to wool

  27. Trace > Fibers > Analysis Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Known Unknown

  28. Trace > Fibers > Analysis Fibers from rug in a van. Fibers found on victim.

  29. Trace > Fibers > Analysis Class characteristics Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed

  30. Trace > Fibers > Analysis Class characteristics Refractive Index – n. The ratio of the speed of light in air or in a vacuum to the speed of light in another medium. Other microscopic properties (PLM)

  31. Trace > Fibers > Analysis Class characteristics Chemical Composition: determined by advanced instrumentation

  32. Trace > Fibers > Cordage Threads, Yarn, Rope, Cordage Smallest component is fibers (staple) twisted together to form thread or is a filament. This thread can then be twisted with other threads to form a thicker thread (string, etc.) This thicker cord can then be twisted with other thicker cords, etc.

  33. Trace > Fibers > Cordage Threads, Yarn, Rope, Cordage Small cords or fibers twisted together to form larger cords • At each step, the number of cords can be counted. • At each step, the twist direction is either “S” or “Z”

  34. Glass • What is glass? • What crimes are glass involved in? • How is glass collected? • How is glass analyzed in the lab?

  35. Trace > Glass What is glass? • Made from fused inorganic materials • Amorphus; not crystalline (molecules not arranged) • Varies in elemental formula • Many shapes and colors

  36. Trace > Glass How is glass involved in crime? • Small fragments can be used as trace evidence (link objects/people) • Crime scene reconstruction

  37. Trace > Glass How is glass collected? • For reconstruction, detailed photographs can be taken or the entire pane of glass is collected.

  38. Trace > Glass How is glass collected? • For trace evidence, usually visually collected with forceps and packaged in plastic bags.

  39. Trace > Glass For reconstruction: Radial cracks Concentric cracks

  40. Trace > Glass For reconstruction: Concentric cracks Radial cracks Concentric cracks

  41. Trace > Glass For reconstruction: Determine the direction of projectile. • When looking at a radial section, conchoidal fractures point back to the origin of the break • Core usually on opposite side of the origin

  42. Trace > Glass For reconstruction: Determine the order of projectiles when dealing with more than one. 2 1 3

  43. Trace > Glass For reconstruction: Determine the order of projectiles when dealing with more than one. 2 1 3

  44. Trace > Glass For trace analysis: Associate unknown glass found at the crime scene with known samples to determine the source. Done with microscopic analysis • Color, curve, thickness, etc. • Refractive index: Determined by placing glass in oils of different refractive indexes

  45. Trace > Glass Refractive index: • Low relief = no outside line R.I. of glass and oil are similar • High relief = thick outside line (Becke line) R.I. of glass and oil are different

  46. Paint • What is paint? • What crimes are paint involved in? • How is paint collected? • How is paint analyzed in the lab?

  47. Trace > Paint What is paint? • Colored chemical coating • Covers cars and houses

  48. Trace > Paint What is paint? Paint contains 3 things: • Vehicle – binds components together • Pigment – gives paint color • Extenders – used to modify gloss, texture, opacity, etc.

  49. Trace > Paint What crimes are paint involved in? • Hit and Runs – paint from car left at scene • Other vehicular accidents • Home invasion – windows; on suspect