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JS 96GY: Trace evidence- Hairs, Fiber and Paint

JS 96GY: Trace evidence- Hairs, Fiber and Paint. Announcements, Assignments and Acknowledgements Learning Objectives (Chapter 7) Hair Describe cuticle, cortex and medulla and 3 growth phases Explain distinction between human vs animal hair List useful macro and microscopic hair features

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JS 96GY: Trace evidence- Hairs, Fiber and Paint

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  1. JS 96GY: Trace evidence- Hairs, Fiber and Paint • Announcements, Assignments and Acknowledgements • Learning Objectives (Chapter 7) • Hair • Describe cuticle, cortex and medulla and 3 growth phases • Explain distinction between human vs animal hair • List useful macro and microscopic hair features • Explain proper collection of hair evidence • Describe the role of DNA typing in hair comparisons • Fibers • Classify fibers • Describe the structure of a polymer • List useful forensic properties of fiber • Explain proper collection of fiber evidence • Paint • Describe the components of paint • Classify auto paints • List those examinations most useful for forensic comparison of paint • Explain proper collection of paint evidence

  2. Assignments and Acknowledgements Collect Assignments- Chapter summaries and extra credit Reminders- Final Exam- Monday 15 Dec 08- 0945-1200 CSI Notebooks due - Weds 10 Dec 08 MUSE workshops- Weds 10 Dec 08 Bring hard copies of summaries this weds 10 Dec and post handouts and powerpoints to Google group Assignments Prepare Student led reviews Study for final exam SOTEs Weds 10 Dec Acknowledgements • Marty Blake- SFPD • Jeremiah Garrido and Larry Turner: SCCCL

  3. Summary 1 • Trace evidence includes Animal (hair), Vegetable (fiber), or Mineral (glass, explosives, gunshot residue) – It is fragile, easily missed and/or lost. • Hairs extend from its root in the follicle into a shaft and terminates at a tip end- Three layers of the hair, the cuticle, cortex and medulla are subjected to the most intense forensic examination - Color, length and diameter • Morphological features distinguish human vs animals • Scale structure, medullary index and medullary shape are important • Medullary shape and the distribution, shape and color intensity of the pigment granules present in the cortex are important forensic features. • Nuclear and mtDNA can be analyzed from hair roots and mtDNA from hair shaft

  4. Summary 2 The quality of fiber evidence is dependent on the ability of the criminalist to identify the origin or narrow down the number of sources Microscopic comparisons of known and questioned fibers at undertaken for color and diameter. Striations on the fiber, delustering particles and cross-sectional shape are examined. Visible light micro-spectrophotometer and FT-IR IR spec is rapid and reliable for identifying the generic class of fibers. Paint consists of pigments and additives suspended in the binder. Auto paint is compared under a stereoscopic microscope for color surface texture and color layer. Pyrolysis GC and IR spec can be used to distinguish most paint binder formulations

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