Batman breaks his code against killing in Injustice: Gods Among Us: Year Three #13. Batman snaps the Joker’s neck while driving him to Arkham Assylum for the umpteenth time. He immediately goes to the police station presumably to turn himself in but don’t expect him to do any real time. That’s because it’s all a dream!
The Dark Knight puts Superman into a magically induced coma after he assumes absolute power over the Earth. It was actually the super dictator that killed the Joker. Superman is drugged and tricked into thinking that Lois was Doomsday. He accidentally kills both Lois and their unborn child but Batman warns him in time in Superman’s dream. Nevertheless, the so-called boy scout is still furious so much so he unintentionally reveals Batman’s secret identity. Superman tells Bruce to stand aside and let him interrogate the Joker about the location of a nuclear bomb hidden in the Metropolis.
“This spoils everything!” Joker tells his archenemy. “Now you’re just a ‘Bruce’ in a bat-suit.”
Batman says he’ll handle the Joker but Superman isn’t impressed with his track record. He ominously assures Clark that the Joker will never hurt him again.
Batman puts the Joker in the Batmobile for a very long ride back to Gotham. He’s less talkative than usual and doesn’t bother to question him about the bomb. Joker jokes he simply wanted some alone time with him. The Clown Prince of Crime explains that all the mayhem he causes is for Batman but he wants to play with Superman some more. He asks for permission like a romantic partner saying they want to see other people. The Joker contemplates killing Superman’s baby but Batman snaps his neck before he can finish the sentence. He appears to turn himself in so it won’t be an inverted plot where Batman goes rogue instead of Superman. In fact, the story arc will end in next chapter when someone wakes Superman. The question is whether the experience of seeing Batman kill will open his eyes or losing his family for a second time will strengthen his resolve.