(Video and image via BleedingCool)
On Kevin Smith's radio show, Grant Morrison discusses why Alan Moore's The Killing Joke is important... because Batman kills the Joker at the end.

(unnecessary foul language... because it's Kevin Smith, I guess)

Like many guys my age into comic books, I got this way back when it was first printed and even met Brian Bolland and got him to sign the thing. But I never interpreted the last few panels as Batman killing the Joker. Apparently this discussion was going on back in the day but was apparently word of mouth rather than on the non-existent internet chat rooms and in blogs (like this one).

Today, legendary letterer Richard Starkings stated on Facebook that he pointed out to Brian Bolland that Batman kills the Joker, as revealed by the abruptly ended laughter.