An obscure villain of the sixties manga incarnation of the caped crusader, Lord Death Man was resurrected by Grant Morrison for the Batman Incorporated storyline, where Bruce Wayne franchised his superhero identity out to vigilantes around the world, all the better to fight international crime with.
In Japan he came across Lord Death Man, an immortal villain who was already waging war on the nation's metahumans by, erm, murdering all of them. So we guess Batman returning that in kind isn't totally unreasonable. Plus it's not technically murder, what with Lord Death Man being unable to die and all. Which is handy, since our hero does have that whole "thou shalt not kill" moral clause going on, which means he can't just shoot his rogues gallery in the head rather than contend with them constantly breaking out of Arkham Asylum.
There's a subtle difference between being immortal and invincible, though. Because Lord Death Man is only the former, meaning that whilst he can't be killed, he just feel pain. So when Batman throws him off the top of a skyscraper, flops his crippled body into a safe and then fires him into space, he's placing him under a level of torture even the CIA would balk at. He's had his spine shattered, then broken again by being stuck in an enclosed space, and now he's doomed to forever orbit the planet, coming back to life, suffocating to death, over and over for the rest of his days.