The Fire Marshal’s office is trying to figure out what sparked a fire in Monmouth that destroyed a mobile home. The fire chief says the fire on Back Street appears have started in the rear of the house, near the furnace. A neighbor spotted the fire about 9:30 a.m. Monday.No one was home. Crews from five towns were called in to knock it down. Some of the fire spread to the grass behind the house, too.We’re told the homeowners are on vacation.The person who’s been watching the place had already left the house by the time the fire began.