If you murder someone then go back into the past and make it as if it never happened--are you still a murderer.
To continue--and, yeah, SPOILERS, Spoilers, spoilers....
In The Butterfly Effect, Evan keeps returning to the past to change it and make it all better. In one of his first trips he ends up saving his girlfriend from her pedophilic abusive father (sort of), while turning her brother into a sadistic criminal. Saving the sister turned her (and apparently by association) Evan into preppies, she a member of the most popular sorority and he a frat boy who dresses in bright yellow jackets.
While it's interesting to speculate why she would be able to watch her father constantly beating her brother and be unaffected (or maybe that's why she's in a sorority--to have the perfect life and learn to ignore bad stuff), that's not relevant to our thoughts today. Back in the ‘present' Evan is happily dating Kayleigh (though apparently before he came back from the past he was a boorish, cheating, jerky frat guy, happily dating Kayleigh). The returned-from-the-past Evan prepares a beautiful dinner for Kayleigh (which she says is not at all like him) but it's ruined by the destruction of his car and the news that Tommy, the sadistic, evil brother is out of prison. As Evan is walking Kayleigh home (and if they're as worried about the brother as they say they are--why are they walking alone through the woods), Evan is attacked by baseball bat wielding Tommy. Evan gets the bat away from Tommy and defeats Tommy. Then, after he's defeated, Evan deliberately beats him to death.
Eventually after several more trips back in time, Evan makes everything more or less all right. We're supposed to forget, I think, that out of four main characters in the story, three of them have been, in one reality or another, murderers.
So here's the question: if you're willing to kill someone in one timeline or alternate reality does that make you a killer in this one? I think the answer is yes. If you did it, and you remember it, you're a killer. Circumstances matter, of course, and the circumstance for Evan is that he meant to kill Tommy. At this point in the movie, Tommy had done some horrible things--killed a pet dog and beat up innocent bystanders and, of course, Evan remembers bad things from other time lines, too. But he still deliberately killed him, not in self-defense, not in panic, by bashing his head in with a baseball bat.
Obviously, you're never going to be punished for killing someone in an alternate timeline that doesn't exist any more. In the ‘real' or final timeline the person is alive. So, is it really murder or is it more like wishing they were dead. Well, it's really murder. You really did it. And it counts.
The more important questions are what does it mean and what do you do about it? This, to me, is more interesting than the question the movie actually asked, which is how do I ‘fix' my life and my girlfriend's life so they're just right? Maybe someday I'll write that story--if I can make it sufficiently unlike The Butterfly Effect. It would also have to incorporate the premise that women are people too and not just objects that men rescue or love or improve the lives of without asking