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27 Cards in this Set

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Scenario: A Thread of Evidence
String of murders of black youth rocked Atlanta in the1980s.
Police gathered a number of unusually shaped fibers.
C. Fiber match to the rug was the key to conviction.
amorphous
without a defined shape; fibers composed of a loose arrangement of polymers that are soft, elastic, and absorbing (for example, cotton)
crystalline
regularly shaped; fibers composed of polymers packed side by side, which make it stiff and strong (for example, flax)
direct transfer
the passing of evidence, such as a fiber, from victim to suspect or vice vers
fiber
the smallest indivisible unit of a textile, it must be at least 100 times longer than wide
mineral fiber
a collection of mineral crystals formed into a recognizable pattern
monomer
a small molecule that may bond to other monomers to become a polymer
natural fiber
a fiber produced naturally and harvested from animal, plant, or mineral sources
polymer
a substance composed of long chains of repeating units
synthetic fiber
a fiber made from a man-made substance such as plastic
secondary transfer
the transfer of evidence such as a fiber from a source (for example, a carpet) to a person (suspect), and then to another person (victim)
textile
a flexible, flat mate- rial made by interlacing yarns (or “threads”)
yarn
fibers that have been spun together
How Forensic Scientists Use Fibers
1. Type of fiber – composition, uniqueness, and so on.
2. Fiber color – often key to matching techniques.
3. Number found – usually the more found the easier the match.
4. Where found – can you place the suspect at the scene?
5. Textile fiber originated from – carpet, upholstery, car, and so forth.
6. Multiple fibers – several types of fibers can be more conclusive.
7. Type of crime – can be the key to fiber transfer
8. Time between crime and fiber discovery – passage of time greatly reduces the effectiveness of fiber evidence.
Gathering evidence
special vacuums
sticky tape
tweezers
Analysis
Nondestructive
polarizing light microscopy
infrared spectroscopy.
Destructive
burning
dissolving in solvents
A. Fiber classification
1. Natural
a. Animal
i. fur
ii. hair
iii. silk
b. Plant fibers

i. seed fibers, example: cotton
ii. fruit fibers. example: coir
iii. stem fibers, example: hemp
iv. leaf fibers, example manila
c. Mineral fibers or asbestos
Man-made fibers
rayon, acetate, nylon, acrylics, and polyesters
Regenerated fibers
i. derived from cellulose
ii. mostly plant in origin
iii. example: rayon
Synthetic polymer fibers
i. petroleum products
ii. non-cellulose based fibers
iii. polyester, nylon, acrylic, olefins
Comparison of natural and synthetic fibers
under magnification, all synthetic fibers have very regular diameters hairs have cuticles
Yarns
Fibers too short to be used to make textiles in their raw state may be spun together to make yarns


Any given yarn will have a direction of twist.



Forensic scientists will identify the twist direction as part of their identification.
Weave pattern
warp & weft
pattern determined by number of threads jumped as weave over and under
Thread count
= The number of threads that are packed together for any given amount of fabric
Case Studies
Case Studies
A. The murder of George Marsh (1912)
B. Roger Payne (1968 U.K.)
C. John Joubert (1983 Nebraska)
A. Irene Good
textile expert