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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?.
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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? • Natural fibers of animal origin • Terms: human = hair; animal = fur • Usually growing (live root)
Trace > Hair What is hair? • Cellular material in the hair shaft (mtDNA) • Good DNA in the hair root for forcibly removed hairs (STR)
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.
Trace > Hair How is hair collected? • Visually by hand or with forceps. • Possibly tape lift. • Packaged in sealed containers.
Trace > Hair How is hair analyzed? Look at class characteristics (microscope): • Color • Medulla, Cortex, Cuticle
Trace > Hair How is hair analyzed? Medulla: • Line down middle of hair • Species ID or human ID • Present, absent, or fragmented
Trace > Hair How is hair analyzed? Cortex: • Color of hair • Species ID or human ID • May contain pigment blotches • May contain air pockets
Trace > Hair How is hair analyzed? Cortex: • Humans = 1 color entire length • Animals = color can vary at root/middle/tip
Trace > Hair How is hair analyzed? Cuticle: • “Scales” on outside of hair • Species ID only • Humans = imbricate
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).
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)
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.
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.
Trace > Fibers Fibers can be classified into three main categories: • Natural (animal, plant, mineral) • Manufactured • Synthetic
Trace > Fibers > Natural Natural Fibers: • Found in nature • Can be artificially colored or treated Cotton Wool Hemp
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
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
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
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
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)
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
Trace > Fibers > Synthetic Synthetic Fibers • Man made • Can also be filament or staple Examples: Nylon and Polyester
Trace > Fibers > Synthetic Synthetic Fibers Acrylics • More common as evidence • Usually in staple form • Staples spun together, similar to wool
Trace > Fibers > Analysis Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Known Unknown
Trace > Fibers > Analysis Fibers from rug in a van. Fibers found on victim.
Trace > Fibers > Analysis Class characteristics Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed
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)
Trace > Fibers > Analysis Class characteristics Chemical Composition: determined by advanced instrumentation
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.
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”
Glass • What is glass? • What crimes are glass involved in? • How is glass collected? • How is glass analyzed in the lab?
Trace > Glass What is glass? • Made from fused inorganic materials • Amorphus; not crystalline (molecules not arranged) • Varies in elemental formula • Many shapes and colors
Trace > Glass How is glass involved in crime? • Small fragments can be used as trace evidence (link objects/people) • Crime scene reconstruction
Trace > Glass How is glass collected? • For reconstruction, detailed photographs can be taken or the entire pane of glass is collected.
Trace > Glass How is glass collected? • For trace evidence, usually visually collected with forceps and packaged in plastic bags.
Trace > Glass For reconstruction: Radial cracks Concentric cracks
Trace > Glass For reconstruction: Concentric cracks Radial cracks Concentric cracks
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
Trace > Glass For reconstruction: Determine the order of projectiles when dealing with more than one. 2 1 3
Trace > Glass For reconstruction: Determine the order of projectiles when dealing with more than one. 2 1 3
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
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
Paint • What is paint? • What crimes are paint involved in? • How is paint collected? • How is paint analyzed in the lab?
Trace > Paint What is paint? • Colored chemical coating • Covers cars and houses
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.
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