LISBON FALLS, Maine — The state Fire Marshal’s Office says a working smoke detector likely would have saved the lives of two young sisters who died when their house caught fire in Lisbon Falls.

Authorities say the fire that killed 11-year-old Natalie Hogan and 6-year-old Kelsey Hogan on Friday started accidentally underneath a second floor bathtub. Investigators are looking at two possible scenarios — a torch that had been used the night before to unplug the bathtub drain, and a light fixture on the first floor under the tub.

The Fire Marshal’s Office says the home had one smoke detector, but the battery had been removed.

The girls’ mother was living in the farmhouse with her six children. Four other children escaped unhurt. The mother was being treated for burns and smoke inhalation.