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Fibers as Evidence

Liberty Christian Forensic Science Background on fiber analysis.
by

Mark Ramsey

on 16 October 2014

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Transcript of Fibers as Evidence

Fiber Analysis at LCSI
Fibers as Evidence
Fibers, like hair shafts, are always class evidence. They are also classified as physical evidence because they are physical material left behind at crime scenes. Fibers are also considered trace evidence which is defined as evidence that occurs when different objects contact one another.

Examples of typical trace evidence include fingerprints, glove prints, hairs, cosmetics, plant fibers, mineral fibers, synthetic fibers, glass, paint chips, soils, botanical materials, gunshot residue, explosives residue, and volatile hydrocarbons (arson evidence).
What class of
evidence are fibers?
Natural
fibers and
synthetic
fibers.


Natural
fibers come from plants or animals.

Synthetic
fibers are "synthesized" from man made materials by chemically creating long chains of repeating molecules called
polymers.
Fibers fall into
TWO
basic classes:
What is "cross transfer?"
What was the first manmade fiber used in textiles?
Which synthetic fiber has a triangular cross-section?
Which fiber is created by the larval stage of a flying insect (Bombyx mori)?
What is a long-chained molecule that is used to make fibers?
What are the tiny holes that polymers are forced through in order to form fibers?
What are the tiny depressions on a fiber caused by chemical treatment?
What is the technique called that identifies substances based on the amount of light that is absorbed when it is passed through a sample?
What two types of wool come from goats instead of sheep?
What types of animal hairs are clothing made from other than sheep or goats?
Fiber Analysis
Facts to know
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What good is collecting fibers if they can't be tied to individuals?
Reminder
What is Class Evidence
?
Fibers convict a famous serial killer
The Atlanta Child Murders (1979 to 1981):
Wayne Williams is thought to be one of the worst serial killers of adolescents in U.S. history. His victims were killed and thrown into the Chattahoochee River in Georgia. Williams was questioned, because he was seen near where a body had washed ashore. Two kinds of fiber were found on the victims.
The first kind was an unusual yellow-green nylon fiber used in floor carpeting. Through the efforts of the FBI and DuPont Chemical Company, the carpet manufacturer was identified. The carpet had been sold in only 10 states, one of them being Alabama, where Williams lived. Thus, the fibers found on the victims were linked to carpet fibers found in Williams’ home.
Another victim’s body yielded the second type of fiber. This fiber was determined to be from carpeting found in pre-1973 Chevrolets. It was determined that only 680 vehicles registered in Alabama had a matching carpet. Williams owned a 1970 Chevrolet station wagon with matching carpet. The probability of both types of fibers being owned by the same person was calculated. The odds against another person owning both carpet types were about 29 million to one. Williams was convicted and sentenced to two life terms.
Reminder:
Locard's Exchange Principle
Locard’s exchange principle states that contacts between people and objects during a crime can involve a transfer of material that is evidence of the crime.
Plant fibers
Plant fibers include:
Hemp
Flax
Cotton
Sisal
Abaca
Coir
Jute
Ramie
Animal fibers
Wool
Camel Hair
Silk
Class evidence can only be associated with a group and not a single source. Examples of class evidence include shoe size, height, hair type, blood type, etc.
Synthetic fibers are man-made:
Most Common in Clothing
Cross Transfer
Cross transfer refers to the fact that when a criminal comes in contact with his environment, evidence is left behind.
Cross transfer of fiber depends on area of contact, pressure and position of person, number of contact passes, fiber composition, fiber length.
Triangular
Cross-Section
Nylon
is very common in carpet and fabric and has a three-sided cross-section.
First
Synthetic Fiber
Nylon
was first mass produced on February 28, 1935.
Nylon Fibers
Silk is created by the silkworm
Silkworms are actually the larvae of a moth.
Polymers
Polymers are long-chain, repeating molecules that form the structure of synthetic fibers.
Spinnerets
The polymer is drawn through the tiny holes in a spinneret to be formed into usable fibers.
Polyester
Polyester has tiny indentations on the surface of its fibers called
"pitting"
caused by the chemical process that forms it.
Spectrophotomety
Spectrophotometry can be used to determine the chemical composition of compounds including fiber evidence.
Goat for it!
Cashmere and Angora goats produce expensive wools.
Camel
Camel hair is used in the production of fabrics around the world.
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