Theory about Nolans Joker

I was watching TDK, I realized that the Joker knows who Batman really is. when the joker was being beaten up he says "for a while I thought you actually were Dent. The way you threw yourself after her" and "does Harvey know about you and his little boogie" and why else would Joker choose to kill Rachael? why not Gordon? Joker probably knew fully well who's party he was crashing. what do you think reddit?