I just got through watching it and for the first time....a clue stuck out like a sore thumb......
I always thought this as well....until tonight. A clue is buried in one of the prank calls. It is the call right after Jess and Peter argue about her pregnancy. She comes home, gets the call, and "Billy" says "Where did you put the baby?". Yes he is talking about Billy-Agnes but this is an interesting comment for the killer to make at that particular time.
I think its meant to convey that the killer is someone very close to them. A very small circle knows about her pregnancy. I know many years ago there were theories regarding the murders being committed by Peter and Chris....and the fact the studio wanted the ending changed to Chris uttering the Billy-Agnes lines certainly wound up giving that theory some traction.
Another thing that allows the possibility of two killers is how the calls sound like they might be coming from more than one person.
Another mystery within the greater mystery is the missing girl that's not related to the main girls in the story.
I love the mystery of this film. Its a very unique slasher.
The end of this always leaves me questioning if the killer is still loose...
There's no questioning it....the killer(or one of the killers) is definitely still alive.
wonder why a sequel was never made ?
Because Clark wasn't going to cheapen his vision with sequels.