Mo. Rev. Stat. § 320.230: Investigations conducted — cooperation with local officials required — may act as peace officers, when, qualifications.

1. The state fire marshal shall conduct investigations and may conduct hearings into the cause, origin, or circumstances of fire losses and shall cooperate with the appropriate fire or police officials of this state or its political subdivisions in investigations of the cause, origin or circumstances of fires, explosions or related occurrences involving the possibility of arson or related offenses.

2. The state fire marshal and the marshal's paid investigators who have attained proper certification as peace officers pursuant to chapter 590 as approved by the director of the department of public safety shall be deemed to be peace officers and shall notify the local law enforcement agency of the existence of the investigators and shall have the power of arrest for all offenses incident to the investigation of the cause, origin or circumstances of fires, explosions or like occurrences involving the possibility of arson, or related offenses, and in connection with any offenses when aiding and assisting the sheriff of any county or the chief of police of any municipality, or their designated representatives, at their request.