When the firefighters’ tasks end, that of the arson investigator begins. Technically, arson has several meanings in both common law and statutory language, but to the arson investigator it means the deliberate setting fire to one's own property or the property of another, for an unlawful purpose. Arson requires two separate and distinct investigations; the first being the one to determine that the fire was indeed arson and the second being a criminal investigation to arrest and prosecute the arsonist. The investigation is difficult in that many times valuable evidence is wholly or partially destroyed by the fire. The investigation is unique too, in that city ordinances and state laws have made two separate agencies equally responsible; the Fire Department and the Police Department. Experience has shown that the most effective arson investigation requires the closest cooperation between the Police Department and the Fire Department's Fire Inspector’s Office.
The Arson Investigation Unit is primarily responsible for assisting in the investigation of all arson fires, suspicious fires, explosions, and the manufacturing of explosives in conjunction with the Kingsport Fire Department Fire Inspector's Office. The Arson Unit is a sub-division, or specialty area, within the Criminal Investigations Division. The purpose of the Arson Unit is to work with the local, county, state, and federal law enforcement and fire agencies in order to successfully investigate and prosecute those individuals involved in arson-related crimes.