I remember two girls going to a convenience store and ask the young guy behind the counter for weed and end up going back to his apartment to smoke it. Then his family comes back unexpectedly and turn out to be murderers (I think). They end up taking the girls captive and drive around some woods until their car crashes when the girls try to fight back or something. They torture one of the girls until she dies and the other swims away through a nearby river back to her parents' house. I think at some point the family kills the girl's parents, but I'm not sure.

I can't remember the name of this movie, but I remember seeing a lot of it on TV once. Thanks!