the killer was....case closed
peter.
1. Yes, peter wasnt there with jess when billy called, but he was there afterwards when jess was informing the police. remember he was calling from the same house, so he got down there quickly.
2 he showed no remorse when finding out about the other girls dissapearence.
3. how could he know she was hiding down in the basement? he had to be damned sure to break the window.
4. at the end, the police officer says the morgue could not pick up all the bodies because there wasnt enough room. this implicates peter was left in the house. there is a scene of an empty bloody bed which is where his body was placed, and afterwards he moved. he never died.
peter=billy