CORINTH — The Maine state Fire Marshal’s Office says the cause of a camper trailer fire that killed a 7-year-old boy can’t be determined due to extensive damage from the fire.

The fire killed Christian Rand, who was found in the burned out camper in Corinth shortly after the fire was reported Friday morning. The boy, who had stayed home from school, was alone.

Fire investigators said today the only source of heat was electric heaters, connected by extension cords to a nearby house occupied by the boy’s grandparents.

The boy’s parents, Amanda and Nicholas Rand, were away at the time of the fire. Investigators say they’re not filing any charges against them.