Ask any comic book nerds and they'll tell you that there are two things that define Batman: With enough prep time, he could take down God himself, and he never, ever takes a life. However, for a guy who supposedly took a vow to never use a gun or kill any of his enemies (thus justifying the continued existence of the Joker), it turns out that Batman has not just murdered several dudes over the years, but done so in gruesome ways that probably made his victims wish that he'd just shot them.
6 Batman Hangs a Mental Patient from the Batplane (Batman No. 1, 1940)
Batman's career in needless, brutal murder started early. In the very first issue of Batman's solo rag, an evil scientist uses a toxic serum to turn a group of innocent mental patients into muscular, out-of-control monsters. The scientist's henchmen are driving one of the monsters to town, planning to set it loose in front of a bank they want to rob. Unfortunately for them, Batman had just finished mounting a brand spanking new machine gun onto the Batplane.
"Rat-tat-tat-tat-tat-tat-tat-tat ... Batman!"
Batman guns down the driver and causes the truck to crash into a tree, but the henchmen actually get off easy compared to what's about to happen to the confused, mentally handicapped mass of muscles in the back: As soon as he falls out of the truck, and before he can hurt a single soul, Batman drops a noose made from reinforced steel and easily snatches the monster by the neck:
He'd been practicing this very maneuver on vagrants for months.
Batman then lifts off the aircraft as the monster desperately struggles to break free from the noose, choking him to death and thus performing the world's first execution by bat-shaped plane. The Batplane then sails smoothly toward its next destination with a few hundred extra pounds of genetically altered dead weight attached, swinging like a grotesque pendulum.
Most people just hang fuzzy dice on the mirror, but whatever.
What's that? "He's probably better off this way"? Actually, Batman, he definitely would have been way better off if you'd just shared the antidote to the serum you'd created moments earlier, but only thought to use on yourself. When the scientist first injects Batman with the serum, he specifically mentions that the monsters' brains are affected by it, so they aren't in control of themselves. There's no guarantee that the cure would have worked on the mental patients, but Batman could have at least tried.
"But what if it doesn't work on them? I can't handle that kind of disappointment."