Okay, so I can't remember in which novel or where I remember seeing this guy, but he was just this average nobody who just wanted to kill Batman for basically no reason, which is why he's so dangerous. Batman would never suspect him and would never know when he'd strike. I don't remember him playing a big part in whatever he was in; I just remember thinking that he was actually kind of terrifying and feeling some genuine pity and fear for Batman's life, that this guy is planning to kill him just to kill him and there's almost no way he could see it coming.
That's all I remember about him, and twenty minutes on Google has turned up nothing. Anybody know who I'm talking about?