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Getting Started : A fiber from a suspect is found on a murder victim. Does this automatically prove the guilt of the suspect? Why or why not?. Focus : How do forensic scientists analyze fibers and fabrics?. Forensic Science NYS Science Standard 4 Learning Targets : SWBAT-
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Getting Started: A fiber from a suspect is found on a murder victim. Does this automatically prove the guilt of the suspect? Why or why not? Focus: How do forensic scientists analyze fibers and fabrics? Forensic Science NYS Science Standard 4 Learning Targets: SWBAT- Define basic vocabulary Explain how criminalists use fibers Identify and describe common weave patterns Describe types of fiber evidence
Atlanta Child Murders • -1979-1981 • -29 children & young adults were • killed or went missing • -1982 Wayne Williams convicted of • 2 murders based in part on carpet • fiber trace evidence • Information about fibers found on the victims was released to the press. As a result Williams began to dump the bodies of his victims into the river where the fibers would be lost. Police were able to stake out the rivers to catch the criminal.
Forensic Fiber Vocabulary • Fiber: the smallest indivisible unit of a textile, it must be at least 100 times longer than wide. • Natural Fiber: a fiber produced naturally and harvested from animal, plant, or mineral sources. • Synthetic Fiber: a fiber made from a man made substance such as plastic. • Mineral Fiber: a collection of mineral crystals formed into a recognizable pattern. • Direct Transfer: the passing of evidence, such as a fiber, from victim to suspect or vice versa. • Secondary Transfer: the transfer of evidence such as a fiber from a source (for example, a carpet) to a person (suspect), and then to another person (victim). • Textile: a flexible, flat material made by interlacing yarns (or threads). • Yarn: fibers that have been spun together.
Introduction • Fibers often fall off and are picked up during normal activities. • Very small fibers easily shed from most textiles and can become trace evidence. • In an investigation, collection of fibers within 24 hours is critical, 95% of fibers are lost after this period of time. • Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.
—Natural Fibers Fiber Classification Animal fibers (made of proteins): • Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles as well as silk.
—Natural Fibers Fiber Classification Plant fibers (made of the polymer cellulose): • can absorb water. • are insoluble in water. • Cotton, hemp, flax
—Synthetic (artificially produced) Fibers Fiber Classification Until the nineteenth century only plant and animal fibers were used to make clothes and textiles. Half the products produced today are artificially produced. Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters. Forensic Science: Fundamentals & Investigations, Chapter 4
Yarns, fabrics, and textiles Weave Patterns Forensic Science: Fundamentals & Investigations, Chapter 4
. . . . . . . . . .Chapter Summary • Fibers are spun into yarns having specific characteristics. • Yarns are woven, with different patterns, into clothing or textiles. • Fibers, trace evidence, are a form of class evidence used by crime scene investigators. • Fiber evidence may be gathered using different techniques. • Fibers may be analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy. Forensic Science: Fundamentals & Investigations, Chapter 4