FARMINGTON, Maine (AP) — A leaking gas line allowed hundreds of gallons of propane to escape before a powerful explosion leveled a building, killing a firefighter and injuring eight other people, officials said Friday.

The building supervisor who evacuated workers smelled propane gas and noticed that the 400-gallon tank was empty, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

The tank had been topped off the Friday before the blast that happened Monday, Sept. 16, at the Life Enrichment Advancing People Inc. center, McCausland said.

Firefighters who went into the building with the supervisor reported the propane gas odor was not pronounced, possibly because the gas had filtered through the soil before entering the basement, he said.

The explosion, which could be heard from miles away, shattered the building and left the scene littered with dust and paper. Eleven nearby mobile homes were rendered uninhabitable, leaving about 30 people homeless.

The building supervisor, Larry Lord, remained in critical condition Friday at Massachusetts General Hospital, a spokeswoman said. Two firefighters were hospitalized at Maine Medical Center, as well.

Killed in the blast was Farmington Fire Capt. Michael Bell. His brother, Fire Chief Terry Bell, was among the injured.

An investigation continues into determine how the propane line was damaged and what sparked the explosion, officials said.

More than 100 interviews have taken place as fire marshals work with the Bureau of Alcohol, Tobacco, Firearms and Explosives and other state and local agencies, officials said.