Or maybe it is Tommy Elliot. After all, Ra's did say, "Who in your life would wish to come back from the dead?". Maybe Tommy had Two-Face get in touch with the Joker to be at just the right spot to make it look like Joker did it, and also had him call Jim Gordon to stop Batman from killing Joker. Between his death and burial Elliot had made plans to be taken to a Lazarus Pit. In the meantime, Batman is looking for Elliots killer and is too busy to pay attention to whatever it is that Hush is doing. I think it might have to do with that RC-60 defoliate or the Lamont Chemical factory mentioned in #608
