CHAPTER OVERVIEW

• Fibers from clothing or hair can be transferred from one person to another or discarded unnoticed at the scene of a crime

• Fiber type and weave pattern are important features noted by forensic investigators

• The presence of unique fibers on suspect’s clothing or belongings does not prove guilt, but it can link the criminal to a crime scene or victim

BIG IDEAS

• Fibers can easily be transferred between people or between people and their environments

• Textiles are created by weaving, or intertwining, yarns that run in opposite directions

• Fiber types can be identified by physical and chemical analysis

Introduction

• Fibers are used in forensic science to create a link between crime and suspect

• Through normal activities– We shed fibers – We picked up fibers

• Fibers are not specific to any one individual and can easily go unnoticed

• Very small fibers are classified as trace evidence if it is direct transfer

• Collecting fibers within 24 hours is critical

How Forensic Scientists Use Fibers

Fiber evaluation can show

• Type of fiber: what is its composition? Is it common or rare? Where does it match in relation to crime scene?

• Color: does the color match suspect clothes found in victims house? Is the type of dye the same?

• Possibility of violence: break in or kidnapping? Each type of crime has an expected pattern of contact between suspect and victim, and crime scene that will be reflected in the transfer of fibers. Only one type or different sources? Carpet or bed sheet? More sources and more fibers indicate longer contact or possible violence.

• Point of origin• Location of suspects

Sampling and Testing

• Shedding—common form of fiber transfer• Microscopes reveal characteristic shapes

and markings• Infrared spectroscopy reveals chemical

structures to differentiate similar fibers• Destructive Testing Methods• Burning fibers • Dissolving fibers in various liquids

Sampling and Testing

Compare fibers found on different suspects with those found at the crime scene

Fiber Classification —Natural Fibers

Animal fibers (made of proteins): • Wool and cashmere from sheep• Mohair from goats• Angora from rabbits• Hair from alpacas, llamas, and

camels• Silk from caterpillar cocoons

(longer fiber does not shed easily)

woven wool

textile

Fiber Classification —Natural Fibers

Plant fibers (made of the polymer cellulose): • Absorb water• Insoluble in water• Very resistant to damage from harsh

chemicals• Dissolvable only by strong acids• Becomes brittle over time

Fiber Classification —Natural Fibers

Plant fibers: • Cotton—most common textile

plant fiber (picture) • Coir from coconuts is durable• Hemp, jute, and flax from stems grow in

bundles• Manila and sisal from leaves deteriorate

more quickly

Fiber Classification —Natural Fibers

Mineral Fibers: • Fiberglass—a fibrous form of glass• Asbestos—a crystalline structure