The only person capable of doing that is Bruce Wayne. He erased Selina Kyle pass. The Joker was probably one of Bruce employees, when Bruce was exposed by an ex employee claiming that he was batman. So the Joker did some digging and put the pieces together. The scars were self inflicted during the time when Raj was spreading the poison in the air. He was fighting it, in order to stay sane he put a smile on face. He was probably a workaholic and everyone always ask him why so serious. His fear probably was that he'll never be happy. He's a clown, clowns will do and say anything to get a laugh, that's why he made up stories about his scars. He's an aristocrat. That's my theory, you don't have to agree with it.