Pretty much the same thing happened in my hometown.
Family that was there trashed the place, including pulling the wiring and as much plumbing as they could get to, including all the baseboard heating.
Local bank hires local guy to clean it up and do repairs on it.
He's working during a late fall cold snap, and is freezing his butt off, so he builds a fire in the fireplace with construction debris. He's somewhere else in the house for awhile, hears weird noises, and finds the living room and kitchen burning merrily...
Fire department says that the fire probably collapsed out onto the hearth just enough to light the carpet. After that, it's all over.