ST. PAUL, Minn. (AP) — Expert federal investigators are joining state and local teams who are working to find what caused a huge fire at a hotel construction site in St. Paul.

Fire caused extensive damage to the five-story Courtyard by Marriott hotel Tuesday and significant damage to a six-story apartment building under construction. The federal Bureau of Alcohol, Tobacco, Firearms and Explosives has sent members of its National Response Team to assist in the investigation.

Special Agent in Charge Terry Henderson says the specialists were called because of the size of the building, the amount of damage and the number of investigative leads.