I. Trace evidence=  Physical evidence found at a crime scene in small but measurable amounts  Examples: hair, glass, fibers, paint, pollen, gunshot.

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Presentation transcript:

I. Trace evidence=  Physical evidence found at a crime scene in small but measurable amounts  Examples: hair, glass, fibers, paint, pollen, gunshot residue, soil, etc.

II. Examination of Trace Evidence uses Microanalysis  Microanalysis= application of a microscope to the observation, collection, and analysis of trace evidence  Purpose= To determine if an association of persons, places, and things can be made AND the strength of that association

III. Instruments of Microanalysis  1. Light microscopes Total magnification = eyepiece mag. (x) objective mag. TM = EP (x) OBJ Amount of detail seen/revealed is related to the resolving power of the microscope...which is the ability to distinguish differences in fine structure.

1. Light microscopes cont.  Types of light microscopes A. Stereo binocular microscope Used in preliminary evaluation of trace evidence Constructed fro 2 separate optical microscopes for observation of each eye simultaneously Utilize reflected light View has 3-D appearance

1. Light microscopes cont.  Types of light microscopes B. Compound light microscope Most often employed with transmitted bright- field illumination Allows to see details of construction of evidence Amoeba magnified 100 x

1. Light microscopes cont.  Types of light microscopes B. Polarized light microscope Attachment to light microscope that allows for plain polarized light Vibrations of normal light are in all directions (360 degrees), but if restrict vibration to one direction, you get plain polarized light Can give better quantitative data (measurements can be made more easily)

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2. Scanning Electron microscope (SEM) Ant magnified ~1500 x  beams of electrons bounced off surface of specimen to produce image  can magnify much more than light microscope... SEM has possible range of 10x to 100,000 x Try it!

3. Microspectrophotometry  Combines microscope with a spectrophotometer so that light absorption properties of a very small sample can be recorded  Helps experts to determine COLOR of a sample... such as with fibers, hair, and painted surfaces