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.
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."
After reviewing the evidence, we can pretty confidently say that Batman is the superhero who holds the record for "accidentally" crushing the most folks to death in junkyards, an oddly specific scenario that so far has taken the lives of three Gotham City residents (that we know of).
The first instance comes in Batman No. 425 from 1988, where the Caped Crusader fights a pissed-off drug dealer seeking revenge after Robin intentionally dropped his brother off a rooftop (we wonder where he learned that trick). After thoroughly lecturing Robin about the sanctity of life, Bat-Hypocrite ends up being chased through a junkyard by the drug dealer and somehow toppling a huge pile of unwanted cars on his ass.
To be fair, the guy did stand there like an idiot while a tower of metal fell on him -- we'd almost believe that Batman didn't really mean to kill him if this was the only time that one of his enemies ended up as bunch of mangled body parts buried under garbage (it isn't).
The second and third instances came two years later in Detective Comics No. 613, in which Batman must deal with the escalating violence between garbage disposal companies (yes, Gotham City is so fucked up, even the trash dudes want to kill each other in turf wars). Once again, the climax of the story leads Batman to a junkyard, where he carelessly leaves himself open to a classic wrestling match move.
"Your present, that is! Happy birthday! Here's a ch-"
Rather than ruin his perfect dentition by taking a chair to the face, Batman kicks his middle-aged attacker and causes him to stumble into another crook, sending them both directly into a conveniently placed garbage grinder.
"Gotta get one of these for the Batmobile."
The ensuing violence inspires the greatest onomatopoeia ever printed in a funny book. Seriously, look at this awful mess:
Not to be confused with "KASWULSH," the Swedish boy band.
Is this the same junkyard as before, and if so, exactly how many of Batman's former enemies are buried there? No one's heard from King Tut recently. At this point it's pretty clear that Batman is doing this on purpose and possibly gets off on crushing human bodies (why else would he come up to the grinder and look into it?). See that white-eyed expression in the panel above? That's Batman's O-face.
Unnecessarily brutal murder is Batman's G-spot.
Batman first became popular at a time when xenophobia was as common in children's entertainment as cute cartoon animals, which, combined with Japan's involvement in World War II, resulted in quite a bit of Asian bashing in those early issues. However, while other superheroes like Superman or Captain America were content with just "slapping a Jap" every once in a while, Batman took a slightly more extreme approach.
Like in this comic, where he pushes a huge statue onto a crowd of Mongols, crushing them to death:
"It's certainly lucky that this statue isn't bolted down or secured in any way!"
That's from Detective Comics No. 39, from 1940. Merely four issues earlier, Batman had kicked a Chinese swordsman into the swordsman's friend, which would not be the last time that he impaled a person on a sword (we'll get to that). Later in the same issue, he pushed their leader out of a window, but that guy turned out to be an American in disguise, so Batman probably wished that he'd just arrested him.
"He was dressed up like an Asian! I didn't know he was people!"
Later, in Batman No. 15 (1943), a scientist shows Batman a simulation of what will happen if you don't buy enough war bonds and Japan invades Gotham City. At one point Batman acquires a rifle, but obviously his vow against firearms forbids him from shooting anyone with it, even enemy soldiers ... so he just throws it at the wheels of a vehicle instead and kills the Japanese occupants in a bloody crash.
"See, Robin? Murder is all about compromise."
And speaking of Batman orchestrating traffic accidents, back in those days this happened way more often than you'd think, and not just in possible Japan-ruled futures. Batman's preferred method consisted of knocking out the driver and jumping off as the car crashed into a pole or fell off a cliff, like in Detective Comics No. 47 (1941) ...
That car predates seat belts, so the Bat just signed that man's death certificate.
... and Detective Comics No. 34 (1939).
"Time to die, evil Dr. Glans!"
Eventually, he just got his own car and stopped hitching rides.