FIBERS

Locard’s Exchange Principle When a criminal comes in contact with an object or person, a cross-transfer of evidence occurs. Suspect may transfer evidence to scene or pick up evidence from scene

Cases involving fibers Any physical struggle between two people Carpet fibers adhering to shoes Hit and run - pedestrian fibers on suspect vehicle More fiber associations, more concrete the evidence Primary and Secondary Transfer

Types of Fibers Natural Fibers Man-made Fibers (synthetic) derived from animal, plant or mineral sources Man-made Fibers (synthetic) manufactured from raw materials or synthetic chemicals

What type of fibers are these?

Natural Fibers Broken into 3 classifications Animal fibers Silk, sheep (wool), goats (mohair, cashmere), camels, horse, rabbits Vegetable Fibers Cotton, hemp, jute, ramie, flax, linen Mineral Fibers asbestos

Cotton Most prevalent natural fiber!! White cotton fibers have no evidentiary value Cotton jean fibers have little to no evidentiary value Microscopic appearance: Ribbon-like shape with irregular twists

White Cotton Fibers

Man-made Fibers Regenerated Fibers – produced from the naturally occurring polymer, cellulose Cellulose = repeating units of glucose rayon Acetate Triacetate

Man-made Fibers (continued) Synthetic Fibers - produced from synthetic chemicals (polymers) Nylon Polyesters Acrylics

Polymers Basic chemical substance of all synthetic fibers Assumes different chemical and physical properties Macromolecules of thousands to millions of atoms Huge chains of repeating monomers Natural polymers also exist

Synthetic Fibers have a very uniform appearance

Collection of Fiber Evidence Post-It notes and paper packets (individual or small numbers of fibers Tape Lifts cover large areas (i.e.. Care seats, victim’s clothing, etc.) ALWAYS collect known samples (if several different carpets in the scene, collect a known from each one) Package items separately to avoid cross-contamination

Natural vs. Synthetic Thru the Microscope Natural fibers Usually have a “twisty” appearance Variable diameter NO delustrant particles Scales and medulla (animal hairs) Cross hatching Synthetic fibers Smooth edges, lengthwise striations Consistent diameter (usually) Very clear or has delustrant particles

Single Fibers Collected onto a Post-It Note

Tape Lifting for Mass Collection of Fibers

Tape Lifts for Mass Collection of Fibers White Background Black Background