Over the last 20 years, writers of the Dark Knight have continued trying to trump each other with the amount of carnage and mayhem the Clown Prince of Crime has caused. And his body count. And then Batman sends him back to Arkham Asylum, where we all know he's going to escape.
Hell, Batman even protected the Joker when a Gotham crime boss hired Hitman to kill him.
So DC hides behind Batman's Code versus Killing to protect a murdering lunatic. I guess whatever state Gotham City is in doesn't have the Death Penalty?!
We're not dealing with Batman comics written for kids, at least in the regular DC continuity, anymore. Having Joker tried for his grisly murders wouldn't be "over the heads" of their audience these days.
No, as far as I'm concerned every time the Joker get outs and kills someone, it's on the Batman's head. He's complicit in the crimes. After all, if you put someone in a sanitarium where they have repeatedly broken out, your aiding and abetting his murders. Isn't the definition of insanity trying the same action and expecting different results? That really does go to support that Batman and Joker are just different sides of the same coin.