There is one case that I've been trying to track down for a while. All I really remember seeing were the Re-enactment scenes of the episode.

It was about this girl in her 20's, and this guy (maybe boyfriend or friend?) stabbed her to death.

I remember during the re-enactment scene it was like in a dark room, and he walked up the stairs and started stabbing her. Then he left the house, got into his car and drove away really fast. Maybe fled the state?

It was a long long time ago, so I don't really remember it all. The scene looked it came right out of a horror movie.

You may be thinking of the Rick Church case. Church attacked his girlfriend Colleen Ritter and murdered her parents. The re-enactment of the attacks did look very much like something out of a horror movie. Church was eventually captured and is in prison. I hope this helps.

That's the one! Thanks! :D