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Trace Evidence

The Trace Unit of the Physical Evidence Section is responsible for the examination of small (trace) particles of evidence left behind during a crime such as hair, fiber, paint, glass, fire debris, gunshot residue and other miscellaneous particles.

 
This kind of evidence is often present in violent crimes like rape, murder, robbery, arson, hit-and-run and kidnapping, as well as other crimes.
 
In the analysis of trace materials, the Trace Unit uses several different instruments and methods described below.

Infrared Spectroscopy
Two different Fourier Transform Infrared Spectrophotometers are used in the Trace Unit.  The two instruments are used to analyze paints and polymers, explosives, fibers and unknown materials.

Inductively Coupled Plasma / Mass Spectroscopy
An Inductively Coupled Plasma / Mass Spectrometer is used in the analysis of gunshot residue.  

Gas Chromatography / Flame Ionization Detection
Gas Chromatography / Mass Spectroscopy

The Gas Chromatograph / Flame Ionization Detector and the Gas Chromatograph / Mass Spectrometer are used to identify ignitable liquids in fire debris cases.

Pyrolysis - Gas Chromatography / Mass Spectroscopy
A Curie Point Pyrolyzer is used to analyze polymeric samples.  Paint, adhesives, tire rubber and other polymers are pyrolyzed and the resulting gas transferred to a gas chromatograph / mass spectrometer.

Scanning Electron Microscopy
A scanning electron microscope/energy dispersive x-ray system (SEM/EDX) is used for high resolution and magnification imaging with enhanced depth of field.  The process results in a nondestructive analysis of gunshot residue particles, paints, metals, powders, and other trace materials.

X-Ray Fluorescence
The Thermo-Electron Quan-X fluorescence system is used in the elemental analysis of glass, larger metal fragments, powders and certain liquids.

Microspectrophotometry
Spectral differences in polymeric samples such as paints and fibers are measured with a using microscpectrophotmetry.

Microscopy
Stereomicroscopes, polarizing light microscopes, and comparison microscopes are widely used in trace evidence analysis.


Physical  Evidence Section - Trace Unit:   Forensic Scientist Manager Pete Ware