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Fibers
Collection, Testing and Determination of
Uniqueness
Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.
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Types of Fiber
• Natural-– Any fiber that comes
from plant or animal sources, examples?
• Image of cotton fibers. •Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.
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Types of Fibers Cont’d
• Synthetic-– Any fiber that is made
in a laboratory, examples?
• Image of nylon.
•Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.
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Testing
• Fibers are generally identified by type of cloth and color by
• Physical Properties– Burn test– Melting test– Solubility– Optical properties– Dye identification
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Burning and Melting Tests
• Place the fiber in a flame and record the results.
• Heat the fiber on a hotplate and record the results.
• Changes in physical properties: color, smoke, smell, etc.
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Solubility Test
• What is it soluble in?
– Strong base
– Strong acid
– other
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Optical Properties
• These are the tests that are currently used to identify fibers.
• Behavior in– visible, – IR, – UV and – polarized light • Image from
www.usgs.gov/
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Identification of Dye
• Thin Layer Chromatography– Separates molecules based on the affinity to
the surface they are placed on versus their solubility in the solvent they are being dissolved in
– Low solubility in solvent and high adhesion to the surface--- does not go very far
2009©Forensic Science Today• Image from www.dps.state.ia.us
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Comparison?• How is the fiber from a scene compared to fiber
from a known source? – All the characteristics found on the known fiber and
the questioned fiber must be identical.
• What does it mean to say they are similar fibers? – Class– Individual
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Characteristics
• High probability of linkage with only one individual.
• One of a kind? unusually made fiber made in very small amount with unusual dye
• Consistent with a group
Individual Class
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Fiber Collection
• Cellophane tape into Petri dish or
• Vacuuming
• Choose container that will prevent loss
• Label and
• Seal
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Comparison of Fibers
• Fibers from victim’s fingernail to known sample from suspect’s sweater.
•
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Control Samples
• From victim & suspects’ homes and vehicles
• Uncontaminated
• Large enough to do testing needed
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