Okay so –
I have a vivid memory of this film and watching it with my grandpa but haven’t been able to find it in literal years. It was a horror, and I’ll list the specifics I can recall.
There was a group of teenagers or young adults in a woodsy, swamp like area. I remember a cabin by a lake with a pier.
They start to be murdered, obviously, and in the end it’s revealed one of the girls is the killer, taking revenge for what I think was her dead sister or something.
There’s a scene where they pull back the covers on a bed and find a skeleton laying in it, as well as a fight scene towards the end where two girls scrap as the innocent tries to get onto a boat parked at the peer.
In the very end we’re given a scene of the girl giving the police a statement at the station. Once she walks out of the station she rips off a wig and reveals she’s actually the killer girl.