It shall be the duty of the Fire Department to investigate or cause to be investigated the cause, origin, and circumstances of every fire occurring in the city in which property has been destroyed or damaged in excess of $50. All fires of unknown origin shall be reported, and such officers shall especially make an investigation and report as to whether such fire was the result of carelessness, accident, or design. Such investigation shall be begun immediately following extinguishment of such fire or as soon as it is determined to be safe to do the same, and the State Fire Marshal shall have the right to supervise and direct the investigation whenever he or she deems it expedient or necessary. The officer making the investigation of fires occurring within the city shall immediately notify the State Fire Marshal and shall within one week of the occurrence of the fire furnish him or her with a written statement of all the facts relating to the cause and origin of the fire, and such further information as he or she may call for.
('72 Code, § 3-114)