Batman's No Gun Policy

Correction:
He beats the living sh*t out of them.
THEN he jails them xD

There's this possibility that he killed the Joker in the end of The Killing Joke. Although it doesn't show clearly, he might had either choked him or broken his neck.

I'd like to think that he snapped his neck.
That ray of light was gone in the last panel.

That's what I thought too!

I'm not a follower of comics (so my opinions and thoughts are completely invalid), but I thought he just wanted to use fancy things he developed himself because he's rich and smart and wants to do things his own way.