In the Golden Age Batman killed the bad guy at the end of most issues, usually with no remorse. One time, though, he said, "This is the only time I've ever been sorry to see a criminal die!" (Because it was a corny story where a bump on the head somehow made the guy turn into Dr. Jekkyl and Mr. Hyde.) Every time Batman would fight The Joker, he would think he killed him only for a panel later to show he somehow managed to survive, unbeknowest to Batman. It even got to the point where Batman and Robin joked about how many times they think they killed The Joker only for them to find out he managed to survive somehow.
The only reason Batman got his no kill rule was because of comics code shit.