Note: You may notice a change in style of my posts, read this post about it.
As we saw in the early issues of Batman, after the death of his parents, Bruce couldn't deal with the fact that their shooting was simply a random act. It had to be an enemy of his parents, the Court of Owls, something. A week after the shooting, Bruce sneaks out of the manor and visits Crime Alley, where he finds a hobo who may or may not have been there that night. In trying to reason with the man, all that happens is Bruce ends up getting conned out of his father's watch.
Bruce spends his next few years in school, but using any of his spare time (and much of his study/class time) to research any connections his parents had, and who would want to kill them. When he returns to Gotham on his 18th birthday, he returns to Crime Alley, pays off another hobo, and finds out where the one who conned him years ago currently lives. Repaying the man a visit, Bruce uses the fact that he's no longer a child to threaten a name (and the watch) out of the man: Joe Chill.
Bruce goes looking for Chill, and eventually finds his apartment. To Bruce's surprise, Joe Chill is just a piece of shit man, with almost nothing to his name. While Bruce angrily tries to get him to spit out who hired him to kill his parents, Chill tells Bruce how he didn't mean to, there was nothing behind it, he just wanted the pearls, and Martha screaming startled him, and it went down hill from there. Bruce ends up pointing an antique gun to Chill's head (Batman Begins style) but can't bring himself to pull the trigger.
Bruce leaves the apartment, trying to cope with the fact that there wasn't some big conspiracy behind the death of his parents. With that thought, and the thought of what other evils lurk in the world, Bruce departs Gotham to begin the journey.