A fiber is form of trace evidence.images.pcmac.org/SiSFiles/Schools/AL/HooverCity...A fiber is form...
Transcript of A fiber is form of trace evidence.images.pcmac.org/SiSFiles/Schools/AL/HooverCity...A fiber is form...
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*A fiber is form of trace evidence.
*Since fibers are so small their transfer often
goes unnoticed
*Types of transfer
*Direct
* Directly from victim to suspect or suspect to victim
*Secondary
* Transferred to suspect and then transferred to
victim
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*The value of the evidence depends on the
uniqueness of the fiber
*Rare fibers are more valuable
*Questions to ask
*What type of fiber is this?
*What color?
*How many fibers were found?
*Exactly where was it found?
* What kind of textile did it come from?
*What type of crime was committed?
*Were multiple types of fibers transferred?
*How much time has elapsed?
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*What common police practice was stopped
because of fiber transfer?
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*Fibers can be collected with:
*Special vacuums
*Sticky tape
*Forceps
*If only a few fibers are found, only tests that
do not destroy the evidence can be used
*Example: Microscopy
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*Fibers are the smallest unit of a textile.
*When fibers are spun together they make a
yarn.
*Textiles are things like clothing, carpets, and
upholsteries. Textiles are made by weaving
yarns together.
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*Fibers can be classified as:
*Natural
* Come from animals, plants, and minerals that are
mined from the ground
*Synthetic
*Man-made
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*Animal Fibers
*Made from proteins like keratin
*Wool is the most common
*Others: cashmere, mohair, angora, and silk
*Usually shed easily
*Plant fibers
*All contain cellulose
*Cotton is the most common
*Usually very short
*Mineral fibers
*Fiber glass or asbestos
*Very fine fibers that are sticky
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*Began in the 19th century
*Half of all fabrics today are produced with
synthetic fibers
*Categories
*Modified natural fibers (regenerated)
* Ex: Rayon
*Synthetic Polymer
*Made from petroleum products
* Ex: Polyester, nylon, acrylic, or olefins
Fibers under a microscope
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*Synthetic fibers are stronger than natural
fibers and are not damaged by microorganisms
*Natural fibers don't break down in the sun and
can withstand higher temperatures.
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*Hair is a form of class evidence unless the
follicle (ROOT) is still attached and DNA can be
recovered.
*Good for excluding suspects.
*Transferred very easily.
*Secondary transfer is common with pet hair
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*Regulates body temperature
*Decreases friction
*Protects against sunlight
*Hair follicles form at five months gestation
*We are born with about 5 million hair follicles
which decrease over time.
*About 2% are on your head.
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*Consists of a follicle and a shaft
*Composed of keratin (a protein) which causes
it to be strong and flexible. * What are the sebaceous gland and papilla?
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*Three layers:
*Cuticle (outer layer)
*Cortex (middle layer)
*Medulla (inner core)
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Humans have imbricate flattened cuticles.
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*Head (circular)
*Brows and Lashes (circular with tapering ends)
*Beard and Mustache (thick and triangular;
double medulla sometimes)
*Underarm
*Body hair (oval or triangular; usually blunt tip)
*Pubic hair (oval or triangular; with buckling)
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Human hair grows .44mm a day.
The length (in cm) divided by 1.3 cm can
give you an estimate of when use
occurred in months.
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