Virginia Department of Forensic Science
The Trace Evidence Section examines fire debris, explosives, paint, hairs, fibers, glass, gunshot residue (GSR), fracture matches, and fabric separations. In addition, the section analyzes unknown substances for identification or comparison.
Specifically, we examine:
- Fire Debris
Extractions are performed and identifications are made using the gas chromatograph (GC) and/or the gas chromatograph/mass spectrometer (GC/MS). Analysis is typically for the presence or absence of petroleum products although other non-petroleum based accelerants may be identified.
Analysis for explosives or explosives residues may include commercial, military or improvised explosive devices. To the extent possible, a determination of construction, ignition/detonation source, origin of materials and the function of the device is made. A variety of procedures and instrumentation may be used.
Paint, polymers and other coatings are analyzed to ascertain probable origin. This evidence may be a vehicular as in a hit and run situation or it may be structural as in a tool being used to pry open a door. The microscopic examination for color, texture and layer structure is extremely important. Instrumental analysis may be performed to determine the organic and inorganic composition of the materials.
- Hair and Fibers
The comparison microscope is extremely important in the analysis of known and questioned hairs and fibers. Additionally, the organic composition of synthetic fibers will be analyzed using infrared spectrophotometry (FTIR) with a microscope accessory or pyrolysis gas chromatography (PGC).
Glass analysis usually involves the comparison of the physical and/or optical properties of known and questioned glass sources. The refractive index (R.I.) of the glass sources is determined using the Emmons Double Variation method. If enough glass is present to reconstruct a pane, often the direction of the impact or sequence of impacts may be determined.
- Gunshot Residue
GSR analysis is performed on evidence from GSR collection kits developed and provided by the Division of Forensic Science. These kits employ sticky tape on a thumbtack-like “stub” that is used to sample the hands of an individual suspected of firing a weapon. Examiners use an automated scanning electron microscope/energy dispersive x-ray system (SEM/EDS) to confirm the morphology and elemental composition of any particles found.
- Fabric Separations
Microscopic analysis is performed on items to determine is separations in the fabric were made by cutting, tearing or normal wear. Often test separations are made to simulate the questioned separations in an item.
- General Chemical
The analysis of unknown substances for identification or comparison purposes can be the most challenging of all examinations. Potentially, every piece of instrumentation that the Section has available may be used to analyze a material. Examples of general chemical evidence types include: pepper sprays or maces, materials used to vandalize vehicles and adhesive tapes. If the evidence is of a type never encountered before, a method for its analysis must be developed.