The Killing Joke

[The Dark Knight]

Batman and the Joker will kill each other in the end. Pretending otherwise is a joke.

Absolutely. TKJ references that with the "perhaps you'll kill me, perhaps I'll kill you, perhaps sooner, perhaps later" commentary. I think the Joker's death at the very least is an accepted eventuality, with TDK Returns and Beyond being two key examples. TDK Returns satisfies my cravings for such a scene the most, because it represents an accumulation of an entire career's worth of restraint falling away in a moment of desperation. Batman is getting stabbed repeatedly, he's bleeding out and thus the Joker forces the issue. It really works well. 

[The Laughing Fish]

I got to be honest, as eerie as the last few panels were, I was never really convinced that Batman killed the Joker in the end. For the interpretation to work, Batman's body language would have to appear more aggressive - posing in a position where one could perceive he is about to attack the Joker. That wasn't the case here. The only thing we see him doing is sharing a laugh. The laughter may have ended rather abruptly once the police siren plays in the background, but it's not enough to interpret that Batman had finally put the Joker down for good.

When you consider that DC Comics would soon incorporate TKJ as a mainstay of Batman continuity, I find it hard to believe they'd approve the Joker getting killed in the end. As far as I can tell, Brian Bolland seems to encourage the belief that the ending is ambiguous, going by reading his foreword in the Deluxe Edition. But Alan Moore made it quite clear that wasn't what he intended.

Plus, Richard Starkings - the letterer who worked on TKJ - also dismissed the theory.

No. They are laughing. Batman is laughing so hard he leans on the Joker for support. The End.

Brian described it to me that way when this craziness first came up in 1986.

http://www.unleashthefanboy.com/comics/batman-doesnt-kill-joker-in-the-killing-jok/68199

For what it's worth, this is the official script that describes the last moments of the book, and it doesn't show any hints of Batman killing the Joker.



It may be a fun theory to talk about it, but judging by the feedback from some of the creators who worked on the book and the lack of context to support the interpretation.