Investigators said that a surveillance camera captured images of a man who was wearing a Dale Earnhardt jacket and ski mask lighting the fire at R&D Self Storage on Neck Road on Monday night.
A passerby spotted the flames in the back of the building and partially put the fire out before firefighters arrived.
Officials say there was no damage to any of the storage locker contents.
Investigators said that a flammable liquid was used to start the fire and the man may have suffered minor burns as a result.
Anyone with information is being asked to call the Maine State Police in Augusta at 624-7076.