Search: who killed batman's parents
Why: I am watching the first movie (Batman). Jack Napier does it. Later, in Batman Forever (my favorite of any Batman movie, by light years), it's just some nameless jerk in an alley. In Batman Begins, it was Joe Chill, who was driven to mugging because of economic poverty.
Answer: According to the comic books, it was originally an unnamed mugger. In the 1940s to 1980s, they referred to this criminal as "Joe Chill." In Detective Comics #235, Batman learns that Chill is not a mere robber, but actually a hitman who has murdered the Waynes on orders from a Mafia boss named Lew Moxon. In the 1994 DC Universe "Zero Hour" re-vamp, it went back to being an unnamed mugger. More recently, in 2006's "Infinite Crisis," Joe Chill was re-introduced as the killer, but he was caught shortly after the murders.
This is what motivates Batman - if he knew the guy's name, he would track him down and bring him to justice. Then his parents would be avenged. But since he doesn't know, his fight against crime will always continue.
Source: Yahoo! Answers
The More You Know: This guy also says:
Joker couldn't have killed the Waynes - for one thing, he's not necessarily that much older than Batman, and Bruce Wayne was a young boy at the time of the crime. Even if he were a man at the time, Joker wasn't necessarily a criminal then - various origins have shown Joker to be a failed stand-up comic who was tricked into helping commit a robbery of the chemical factory where he was transformed.