Chapter 8 Hair, Fibers, And Paint

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Presentation transcript:

Chapter 8 Hair, Fibers, And Paint

Introduction HAIR FIBERS AND PAINT Physical evidence in a variety of crimes Not yet possible to individualize human hair to any single head or body through morphology Still has value as physical evidence HAIR FIBERS AND PAINT

Introduction HAIR FIBERS AND PAINT Properly collected and submitted to the laboratory Accompanied by adequate number of standard or reference samples Provides strong corroborative evidence for placing individual at crime scene HAIR FIBERS AND PAINT

Fiber Evidence

Types of Fibers: Natural Fibers Derived in whole from animal or plant sources Wool Mohair Cashmere Furs Cotton Animal fibers: hair Cotton: most prevalent HAIR FIBERS AND PAINT

Natural Polymers Figure 8–10 Starch and cellulose are natural carbohydrate polymers consisting of a large number of repeating units or monomers.

Types of Fibers: Man-made Fibers Manufactured Regenerated fibers Manufactured from natural raw materials Rayon, acetate, and triacetate Synthetic fibers Produced solely from synthetic chemicals Nylons, polyesters, and acrylics HAIR FIBERS AND PAINT

Types of Fibers: Polymers Macromolecules Synthetic fibers Repeating units known as monomers HAIR FIBERS AND PAINT Figure 8–9 The chain-link model of a segment of a polymer molecule. The actual molecule may contain as many as several million monomer units or links.

Fiber Evidence Identify the origin of the fiber Or at least narrow the possibilities to a limited number of sources Fabrics that can be exactly fitted together at their torn edges = fabrics were of common origin HAIR FIBERS AND PAINT

Fiber Evidence Microscopic comparisons between questioned and standard/reference fibers color and diameter characteristics comparison microscope HAIR FIBERS AND PAINT

Fiber Evidence HAIR FIBERS AND PAINT

Acrylic

Polyester

Cotton

Wool

Fiber Evidence Other morphological features for comparing fibers are Lengthwise striations on surface of fiber Presence of delustering particles that reduce shine Cross-sectional shape of the fiber HAIR FIBERS AND PAINT

Fiber Evidence Compositional differences Dyes that were applied to fibers during the manufacturing process Microspectrophotometer Chromatography of pigment Chemical composition of fibers Birefringence: crystalline property of fiber HAIR FIBERS AND PAINT

Burn Test HAIR FIBERS AND PAINT

Burn Test HAIR FIBERS AND PAINT

Burn Test HAIR FIBERS AND PAINT

Methods For Fiber Comparison Visible light microspectrophotometer Compare colors of fibers through spectral patterns. Chromatographic separation: dye composition Generic class of fibers Infrared spectrophotometry Polarizing microscope: characteristic index of refraction HAIR FIBERS AND PAINT

Collection and Preservation Investigator’s task Look for minute strands of fibers Identify and preserve potential “carriers” of fiber evidence Relevant articles of clothing Packaged carefully in separate paper bags If necessary to remove a fiber from an object Use clean forceps Place in a small sheet of paper Fold and label the paper Place the paper packet inside another container HAIR FIBERS AND PAINT

FBI Hair Paper http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm

Summary