Forensic Science: Fiber Evidence Part 1 Natural Fibers

Fiber Evidence Part 1-Natural Fibers

Lesson Objectives

• Describe what fiber is

• Describe the two broad categories of fibers

• Distinguish between different types of natural fibers

Case Study-The Atlanta Child Murders (1979-1981)

• From 1979-1981, 29 children and young men in Atlanta, Georgia, were abducted, murdered, and left abandoned

  • All the murders followed the same pattern, leading police to assume one perpetrator

• FBI Analysts brought on to the case predicted the next location where a body would be disposed of, and staked it out

  • 23-year-old Wayne Williams was found dropping a large bag into the river, which could not be recovered

    • Two days later, a body was recovered outside of a bag, a distance from where the body was dropped

Case Study-The Atlanta Child Murders (1979-1981)

• Investigators brought Williams in for questioning and obtained warrants to search his home and car

  • Could not find any biological evidence, but found rope that was similar to the rope used to tie up victims, and a rare and unique fiber from Williams carpet matched fibers found on many of the victims

• Of the possible 29 murders, prosecutors felt they only had enough evidence to bring Williams to trial for two of them

  • Was convicted of both and sentenced to life in prison

Case Study-The Atlanta Child Murders (1979-1981)

• Williams maintains that he is innocent of all murders and claims that he is a victim of a conspiracy to frame him

• Modern DNA Techniques have been brought forth to test old evidence

  • Results were not able to say definitvely that he did it, but eliminated 99.5% of the entire population and 98% of the African American population from being suspects

  • DNA Testing on Animal Hairs found on some of the Victims indicates that they were around Williams' pet dog at the time of their death

• Some still question whether he is truly guilty of all 29 or more murders

  • The only "evidence" available is that the murders stopped after he was arrested

Introduction to Fiber

• Fiber: The smallest indivisible unit of a textile

  • Must be at least 100x longer than wide

  • Can be natural or synthetic

  • Usually twisted around each other/bound together to form a thread or a yarn

Units of Fiber- Yarns

• Yarns: Fibers that have been spun together

  • Made from fibers too short to be used in the raw form

  • The number of threads in a yarn varies depending on what it is being used for

    • rope is a very big yarn

  • It can be Natural, Synthetic or a combination

  • Has an identifying twist

Larger Units of Fiber

• Fabrics: cloth material made up of fibers woven in a distinctive manner

• Textiles: fabrics and fibers woven together in a distinct pattern

  • Some textiles have a pattern that is too hard to see

    • Felt

• Order of Complexity:

  • Fiber→Yarn→Fabric→Textile

Fiber Classification

• Fibers are split into two major categories:

  • Natural Fibers: from animals, plants, & minerals in the ground

  • Synthetic Fibers: Fibers made through chemical means

Natural Fibers-Animal Fibers

• All Animal Fibers are made of proteins

• Fur

  • Is treated skin and NOT a textile

  • Used for exterior clothing

    • Coats and Gloves

Natural Fibers-Animal Fibers

• Hair

  • Made up of amino acid chains

  • Most commonly used animal fibers

  • Harvested through clipping or brushing with little harm to the animal

  • Used for many types of clothing textiles

Natural Fibers-Animal Fibers

• Silk: Comes from insects

  • Bombyx mori: The domestic Silk Moth

    • Creates a cocoon that must be unwound by hand

    • Has a triangle shape that scatters light like a prism

  • Spider Silk: The strongest material on Earth

  • Very expensive to produce

  • Sheds very few fibers

  • Mainly used in clothing, occasionally bedding

Reorder

Put the following terms in the order of least complex to most complex

• Fiber

• Yarn

• Fabric

• Textile

1

2

3

4

• 1
• 2
• 3
• 4

Multiple Choice

True or False: The number of Fibers in a yarn has little impact on how a yarn is used

• True

• False

Multiple Choice

Which type of animal fiber would you not expect to be found in a bed sheet

• Fur

• Hair

• Silk

Multiple Choice

True or False: All Textiles have a distinct pattern that is easy to see

• True

• False

Multiple Choice

What are all animal fibers made out of?

• Keratin

• Cellulose

• Proteins

• Threads

Natural Fibers-Plant Fibers

• Come from specialized cells in plants

  • Put into groups based on where the cells are

• show a lot of variety

  • Amorphous: Without a defined shape

    • fibers composed of a loose arrangement of polymers that are soft, elastic, and absorbing

Types of Plant Fibers

• Polymer: A long chain of repeating molecules

  • Many different types

  • All Plant Fibers are made of Cellulose

    • Repeating pattern of Glucose

    • Can absorb water without dissolving

• The Cellulose in plant fibers makes it easy to recognize from animal fibers

• Tend to be very short

Seed Fibers

• Seed fibers: Found in seeds

  • Cotton is the most commonly used plant fiber

  • Easy to grow, harvest, weave, & dye

  • Very few concerns with allergies

  • In many clothes and textiles

Fruit Fibers

• Fruit fibers: Found in the fruits of plants

  • Coir: comes from the outer shell of coconuts

    • Is very durable and waterproof

      • Used for baskets and mats

Stem Fibers

• Stem fibers: Found in the stems of plants

  • Grow in Bundles that extend the entire length of the plant

• Most common: Flax (aka Linen)

  • Smooth & Shiny

  • Feels cool in warm weather

  • Crystalline: regularly shaped; fibers composed of polymers packed side by side, which make it stiff and strong

• Other types:

  • Jute: Used for Rope and twine

    • too coarse for clothes

  • Hemp: Used for Rope and clothing

Natural Fibers: Plant Fibers

• Leaf fibers: Found in the leaves of plants

  • taken from the surface of leaves

  • are often very rough and uncomfortable for clothing

  • deteriorate quickly

  • used for ropes, twine, & netting

Natural Fibers: Mineral Fibers

• Neither protein nor cellulose

  • May not even be polymers

• tend to be extremely short and brittle

• Asbestos: a mineral that naturally occurs in rocks

  • is durable, but sheds particles easily

  • Carcinogenic and not used anymore

Multiple Choice

What are all plant fibers made out of?

• Keratin

• Cellulose

• Proteins

• Threads

Multiple Choice

If you want to make clothing which type of of fiber would you be most likely to use?

• Seed

• Fruit

• Stem

• Leaf

Multiple Choice

Coir is an example of which type of fiber?

• Seed

• Fruit

• Stem

• Leaf