Rent The Butterfly Effect 3: Revelation (2009)

Sam Reide can travel back in time and makes his living helping to identify killers to the police. However if he changes anything, deliberately or accidentally, the "butterfly effect" causes history to change. When he returns to the present, things are often completely different and he has no clear memory of what happened. When his girlfriend is murdered he "breaks the rules" by trying to find the killer but, in doing so, he ends up changing his own history. Every attempt to fix the resulting change further scrambles his memory and creates worse problems...