Trace Evidence

Fibers

Sources

• Carpets, clothing, linens, furniture, insulation and rope

Direct Transfer

• Fibers transferred directly from victim to suspect or suspect to victim

• Example: fibers from a victim’s shirt found on the suspect

Secondary Transfer

• Fibers from a source on a person and then transferred to another source or person

• Example: fibers from carpet transferred to suspect and then transferred to a victim

Investigating Fibers

• Within 24 hours, 95% of all fibers are lost from a crime scene.

• Only fibers that don’t belong in a scene are collected.

Fibers as Evidence• Value depends on uniqueness

• Ask questions about:– Type of fiber– Fiber color– Number of fibers found– Where the fiber was found– Textile the fiber originated from– Multiple fiber transfers– Type of crime committed– Time between the crime and

discovery of fiber

Sampling and Testing• Gathered with special vacuums, sticky tape,

and forceps• Must record where the fibers are found• Polarizing light microscopy – looks at fibers

with specific light wavelengths• Infrared spectroscopy – beam of light shoots

at fiber and reflects, how it changes reveals the chemical structure

• Burn Tests• Dissolving fibers in various liquids

Textiles

• Most common form of fiber evidence is shedding of a textile

• Clothing, carpets, upholstery

• Made of yarns

• Yarns made of fibers

Fiber Classification

• Natural

• Synthetic

Natural

• Come from animals, plants, and minerals

Animal Fibers • Made from proteins• Fur is a good donor but not a textile• Most common from animals is hair

(wool, mohair, cashmere, angora, hair from camels)

• Hair used in textiles is usually spun loosely for comfort, also sheds more easily

Animal Fibers• Silk is collected from Bombyx mori

• Reared in captivity and unwound by hand

• Shimmering appearance comes from triangular shape of fiber which scatters light like a prism.

• Do not shed easily because they are long.

Plant Fibers• Made of cellulose, which is very

different from proteins• Absorbs water but will not dissolve in

it.• Very resistant to harsh chemicals• Cotton is most popular• Fibers are short and become brittle

over time, so small pieces of fiber are shed often.

Plant Fibers• Seed Fibers – cotton

• Fruit Fibers – Coir found from the covering surrounding coconuts

• Stem Fibers – Hemp, jute, flax, linen

• Leaf Fibers – Manila from abaca and Sisal which is used for ropes and twines

Mineral Fibers

• Fiberglass – very short, weak and brittle, stick to skin very easily because they are fine

• Asbestos – long, thin fibers; very durable so used in tiles, shingles, siding, and fire-resistant clothing

Synthetic Fibers

• Rayon, acetate, nylon, acrylics, and polyesters

• Changing size of spinnerets changes shine, softness, and feel

Comparison of Natural and Synthetic Fibers• Synthetic fibers are stronger than

natural fibers and are not damaged by microorganisms.

• Synthetic fibers do deteriorate in sunlight and have lower melting temps.

• Cotton – flattened hose appearance with blunt points, hollow core

• Flax – bamboo stick appearance, straight with angles

• Silk – does not taper, no internal structures

• Wool – surface scales visible, hollow core, tapers to fine point

• Synthetic – uniform in diameter, surface treatment may appear as spots, stains, or pits, generally straight

Flax (top) Cotton (bottom) Silk (top) Wool (bottom)

Yarns

• Sometimes made with a blend in fibers for certain qualities

• Rope is one big yarn

• Identify twist direction

Textiles• Lengthwise yarn (warp) side by

side and close together

• Crosswise yarn (weft) woven back and forth in specific patterns

• Types: tabby (plain), twill, satin

• Patterns expressed in numbers:– Tabby 1/1 (weft goes over 1 warp

and under one warp)– Twill 3/1 (over 3 and under 1)