HOLDEN — Fire investigators are trying to discover what caused a massive fire Tuesday that destroyed an expansive home on Balsam Drive and resulted in two floors collapsing inside the building, Sgt. Tim York of the State Fire Marshal’s Office said on Friday.

Investigators were at the scene the day of the fire and again on Thursday, and “had to figure out how best to do [the investigation] safely,” he said.

After doing an initial study, fire investigators decided to include experts from the state who are not available until next week.

“We will not know anything about it until Tuesday,” Jan. 11, York said. “We have a state electrical inspector coming, and Tuesday will be the day they will be there.”

A couple of passers-by saw thick, black smoke billowing above Wiswell Road on Tuesday morning and went to investigate.

Brook Hardy, whose parents live nearby, and resident Ronald Treat, who lives on Copeland Hill Road, arrived at the same time and found Shane Geiser — with his large yellow Lab, Alley — on top of his house trying to get away from the flames.

Alley’s barking is credited with awakening Geiser, who went out his second-floor bedroom window with the dog onto the home’s wrap-around porch. Hardy and Treat are credited with helping to get the homeowner and his dog to safety on the ground.

Shortly after firefighters arrived, “the first floor collapsed into the basement and the second floor followed shortly, collapsing onto the first floor,” Holden Fire Chief Jim Ellis said from the scene Tuesday afternoon.

Firefighters from Bangor, Brewer, Dedham, Eddington, Orrington, Hampden and Milford assisted crews from Holden in fighting the blaze, he said.

Geiser lived at the home with his wife, Ann, and their three children.

Geiser, a local carpenter and painter, was treated at Eastern Maine Medical Center in Bangor for smoke inhalation and released Tuesday afternoon. He thanked the two good Samaritans who helped him and Alley off the roof and the firefighters who helped put out the fire.

“We’re really grateful,” he said by phone Tuesday night.