FARMINGTON, Maine — The State Fire Marshal’s Office says a leak in a propane line caused the deadly explosion at the LEAP building in Farmington on Monday, Sept. 16 that killed one firefighter and injured seven other people. 

Investigators say they found a significant leak in the propane line which was buried under the paved parking lot. Normally, propane has an odor added to it, but investigators believe the odor dissipated as it filtered through the soil under the parking lot. 

The propane line went from an outside propane tank located at the rear of the property, under the parking lot and into the basement of the building.

RELATED: Gas supplier identified in Farmington explosion as investigation continues

Capt. Michael Bell died in the explosion which injured seven others. Two firefighters, Capt. Scott Baxter and Chief Terry Bell, are still at Maine Medical Center as of Friday, Sept. 27. LEAP's maintenance supervisor, Larry Lord remains in critical condition at Mass. General as of Friday. 

RELATED: Farmington conditions: Capt. Baxter serious; Chief Bell fair; Lord critical

The propane tank had been filled on Friday, Sept. 13, with nearly 400 gallons of propane, but the tank was empty on Monday morning prior to the explosion when Lord examined it with another LEAP employee. 

RELATED: MDOT creates vehicle plate to honor Capt. Michael Bell who died in Farmington explosion

Investigators say Lord was in the basement with Farmington firefighters “TD” Hardy, Joseph Hastings and Scott Baxter when the explosion took place. 

Fire Capt. Michael Bell was on the first floor, Fire Chief Terry Bell was near the rear door of the building, and Deputy Fire Chief Clyde Ross and Firefighter Ted Baxter were outside the building in the parking lot.

Investigators continue to try to determine how the line was damaged and what sparked the leaked propane. 

The propane was used in the building as fuel for the furnace and water heater.

More than 100 interviews have taken place as investigators with the fire marshal's office continue to work with the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), Farmington Police and Fire Departments and the Maine Solid Fuel Board.