1 / 63

Trace Evidence Part II

Trace Evidence Part II. Summary. Microscopic Analysis Types of Trace Evidence. Glass Hair (fur) Fibers. Paint Soil Gunshot Residue. Hair. What is hair? What crimes are hair involved in? How is hair collected? How is hair analyzed in the lab?. Trace > Hair. What is hair?.

branden-gonzalez
Download Presentation

Trace Evidence Part II

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related