Medical Examiner

Trace Evidence

The Trace Evidence Section examines physical evidence submitted in criminal cases including homicide, sexual assault, burglary, vehicular hit and run, arson, and explosions. Trace evidence includes items such as hair, fibers, glass, paint, fire debris, flammable liquids, and explosive materials. However, investigative agencies may request special analyses on a variety of other materials such as soil, adhesives, and plastics. A good Trace Evidence Examiner has a broad knowledge of various types of evidence and the instrumental application that may accompany analysis.

Often the examination of trace evidence is a comparison between a questioned item to a known item. Analysis of many trace evidence items requires a thorough microscopic examination. The microscopic comparison of hairs is often used to include or exclude hair evidence for the purpose of further analysis through DNA testing. Instrumental techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Gas Chromatography Mass Spectrometry (GCMS) and Scanning Electron Microscope / Energy Dispersive Spectroscopy (SEM/EDS) are utilized to identify the chemical properties of materials. For example, FTIR is useful in the identification of fibers, GCMS identifies the presence of ignitable liquids, and SEM/EDS indicates the elemental profile for certain types of samples.

The investigation of fire and explosion scenes has become an important role of the Trace Evidence Section. Members of the trace section provide assistance to the Allegheny County Fire Marshals Office, The City of Pittsburgh Arson Unit, City and County Explosives Ordinance Disposal Units and the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives Agency in the examination and collection of evidence from fatal fire scenes, suspicious fires and explosions. This approach is beneficial to all offices in that the forensic scientists and investigators share information gathered at the fire or explosion scene to postulate theories and retrieve the best evidence for laboratory analysis. Also, the Allegheny County Fire Marshals canine team participates in a laboratory testing program to ensure quality control between positive canine hits at fire scenes and laboratory results when analyzing fire debris for ignitable liquids. This section is involved with professional organizations such as IABTI (International Association of Bomb Technicians and Investigators), PAAI (Pennsylvania Association of Arson Investigators) and MAAFS (Mid-Atlantic Association of Forensic Scientists) which provide continuing education in areas of law enforcement, terrorism and the scientific community.

This section participates in annual proficiency testing through Collaborative Testing Services Forensic Testing Program.