Ch. 4

Fibers

Casey Anthony (fiber/duct tape) beginning and 6 ½ min in

Saferstein and Trace (several min in)

Fibers

The value of fibers as evidence depends on narrowing their origin to a limited number of sources.

Fibers are a form of trace evidence that is transferred between individuals and objects during a crime- used to corroborate other evidence that is found

Important in these types of cases:

HomicideAssaultSexual offense (transfer between

people)Hit and run (fibers adhere to vehicle)

Types of Transfer

Direct Transfer: passes directly from object to victim or vice-versa

Secondary Transfer: transfer from a source to a person then onto another person

Problems:

Mass production of our garmentsNeed to calculate probabilities of how

many people would own that fiberEarly collection is critical, w/in 24 hours

95% of all fibers will have fallen from victim or lost from scene

Types of Fibers: Natural(depends on color and morphology)

1 . AnimalHair: Sheep, goats, camels, muskrat

(Use animal hair ID methods)Webbing: silk (from caterpillar cocoons)

llamas, alpacas, woven into textilesFur: mink, rabbit, beaver

2. PlantSeed Fiber : Cotton cellulose(has ribbon

like twists at irregular intervals, Dyed cotton provides more evidential value than white cotton)

Fruit Fiber: coir- fibers on coconut shell (used for doormats, baskets)

Stem Fiber – jute, hemp, flax (linen)

Mineral Fiber – fiberglass, asbestos

Man-Made

Increase in amount since 1930’s1000’s of fibers under diff. TrademarksGet regenerated or syntheticRegenerated fibers: made from natural

raw materials (ex. Rayon cellulose & nitric acid), made by forcing material thru holes of spinnerets

Synthetic Polymers

Synthetic man-made fibersMade thru polymerizationEx. Nylon (1st marketed synthetic

polymer), polyester, acrylics, olefins

How is Polyester made?

Analyzing Fibers

Look at: Type of fiber Fiber color # of fibers found Where they were found, Textile it originated from Type of crime committed Time between crime and discovery of fibers

Types of Instruments Used:

Infrared Spectrophotometer- Measures the quantity of radiation that a particular material absorbs

Microspectrophotometer -Spectrophotometer w/ a light microscope attached (get spectrum analysis also)- 1500x

Polarizing Microscope -Study materials that have double indices of refraction (birefrigence)

Aspirin

Microspectrophotometer

Identification & Comparison of Man-made fibers

Fibers are class evidence, forensic significance depends on location, number & nature of fiber

Fabrics that can be exactly fitted together are of obvious common origin

Common analysis: side by side comparison of control and crime scene fiber

Color & diameter are obvious points of comparison

Other Characteristics:

Striations (lengthwise or surface) Delustering agents (TiO2-reduces shine)

Cross section- see if unusually shaped Weave Pattern - look at the warp/weft (plain,

basket, satin, twill, leno) Dye composition- use microspectrophotometer Chemical composition- see what broad class

of chemical it belongs to, use infrared spectrophotometer

Polymeric structure (Ex. 200 samples of acrylic fall into 24 diff. Groups)

Physical properties: crystallinity,index of refraction, birefringence, polarizing properties, absorbance