In issue 0 he finds out at the computer in the cave (Bruce likely had made a search about it before he went for patrol) that Catherine was still alive in the middle east and leaves alone to go after her. It`s implied (supposely to make Joker`s account in the next story all the more disturbing) that it was a set up because the Joker was there when he reunited with his mother at her tent (that doesn`t mean it was a set up from her part, course only that it`s made to look like it is).
Dark points at the red haired woman at his funeral (page 17) being Catherine, having been shielded by Jason and managed to escape alive and that it was a dropped plot point from Loedbell. I wouldn`t know but Dark does engage somewhat with the L on Twitter so it might be so.