To bookend FJL's BD greetings with accounts of chilling murders seems a bit unseemly on my part, but here goes for TOD:
For me, murders that involve torture are the ones hardest to watch (make me cringe and look away and hide my eyes) -- like in the Saw movies -- some of the most disturbing, and you don't even see them committed, you see what the cops see when they walk in, are the ones in the movie Seven (haunting, creepy, gruesome, shocking, etc., etc.).