fibers chapter 6. fibers fibers are made up of many filaments twisted or bonded together to form a...

FIBERS CHAPTER 6

Fibers

• Fibers are made up of many filaments twisted or bonded together to form a thread.

• Along with hair, fibers are the most common type of trace evidence left at a crime scene.

• They are considered class evidence, but the evidence can be probative by creating connections and associations.

Sources and types of fibers• Sources of fibers include animals, plants, or synthetic.• Fibers are used to make clothing, carpeting, rope, string,

or nets.• Fabric is made from fibers and each fabric has its own

unique characteristics.• Fabrics are made by weaving, knitting, crocheting,

knotting, or felting.

Weaves• In a weave the lengthwise yarn is called the warp, and the

crosswise yarn is called the weft.• The warp is usually stronger, smoother, and more even

than the weft.• Often the warp and the weft are made of different

materials and are referred to as a blend.• Natural fibers include cotton, wool, hemp, and silk.• Artificial fibers include nylon, polyester, and acrylics.

Chemical Structure of Fibers• Fibers are made of polymers. Wool is composed of

polypeptide chains of amino acids that combine to form keratin.

• Silk is a protein that is produced by the larvae of a moth.• Cotton is a plant fiber made of cellulose.

These 2 functional groups make up what type of organic molecule?

Synthetic Fibers• Common synthetic fibers include – polyesters such as

dacron, nylon, and acrylic. See figure 2.• Polyesters are used in the production of:

Fiber Analysis• Forensic evidence of fibers is based on their physical and

chemical characteristics.• Types of analysis include;

-Microscope investigation

-Burn test

-Chemical test

-Density test

-Refractive Index Test

-Fluorescent Test

-Dye Analysis

-Chromatography

Fiber Transfer• Fibers can be used as trace evidence.• Factors that affect transfer include – how long fibers

remain on victim, fibers that can be transferred and then later lost….

• Make a list of other factors that can influence the transfer of a fiber.

Fiber transfer in OJ Simpson Trial• Fibers from blue knit ski cap allegedly worn by Simpson

the night of the murder found on his wife Nicole and Ronald Goldman.

• Cotton fibers from Goldman’s shirt found in Simpson’s bedroom.

• Fibers found on ski cap found at the crime scene and on the bloody glove found behind Simpson’s house were similar to the carpet fibers from Simpson’s Ford Bronco.