The FBI launched a hunt for four Chinese immigrants last week after receiving a tip that they might have been plotting to explode a dirty bomb in Boston. None of the suspects appeared on terrorist watch lists, and the FBI stressed in a statement that it had little to go on other than an unknown and uncorroborated source regarding an unspecified potential threat. Gov. Mitt Romney said there was no reason for panic. I am going to be sleeping in my bed in Massachusetts tonight and I feel perfectly safe doing so, he said. Days into the manhunt, one FBI official said the informant might have fabricated the story as payback after the immigrants failed to pay him for helping to smuggle them into the U.S.