Investigation files used in prosecuting suspected arsonists before justices of the peace, juvenile, municipal, and circuit courts, and the state Supreme Court. Included are the Deputy State Fire Marshal's reports to his supervisor, adjusters' reports, field notes, testimony of witnesses, legal papers related to hearings and court prosecutions, newspaper clippings, maps and diagrams, photographs and other evidence, and correspondence among members of the Department, the Attorney General's office, insurance companies, local officials, and informers. Also included are files regarding gambling and liquor license violations.

This file was weeded down to court cases, plus some additional investigations which did not result in court cases, but concern possible World War I hysteria against foreigners, bias against minorities, religious prejudice, various types of "infernal machines" important policy decisions by the State Fire Marshal and the Attorney General, suits for slanders against the Fire Marshal and witnesses in civil court cases, illegal operations of stills during Prohibition, fires to cover larceny and murder, and other cases.