A man was stabbed Sunday afternoon when he opened the door and was attacked by a man he claimed he did not know.The victim, William Murphy, sustained a pair of three-inch lacerations to his forearm and leg. He was treated at Saint Thomas River Park Hospital. His assailant remains at large, a case Sheriff Jackie Matheny says may remain unsolved.“He wasn’t cooperative,” Matheny said of the victim, who did not give investigators much information about who stabbed him.