I watched The Stepfather (2009) yesterday, starring Dylan Walsh, Sela Ward, Penn Badgley and Amber Heard.
It was billed as a crime mystery, but there's really nothing mysterious about it; you know who the sociopath is right from the first scene - the stepfather of the title. This is a remake of the 1987 movie starring Terry O'Quinn, who usually does a nice line in sociopaths.
Not a brilliant movie, not bad though.
But why do characters never do the obviously sensible thing? If you thought your good friend was living with a sociopathic murderer, would you drop her a voicemail or email saying you planned to get the guy checked out, or would you just get the guy checked out?