Black Christmas

Always at least one step behind, the police bust into the sorority house cellar to find Jessica (Olivia Hussey) slipping into unconsciousness, the dead body of her mentally unstable boyfriend Peter (Keir Dullea) lying on top of her. In the grand tradition of law enforcement latching on like grim death to the most obvious suspect in spite of said suspect's actual innocence, they assume that he was the murderer and that she killed him in self-defense. A cursory search of the house uncovers the bodies of but two of the victims while a variety of concerned citizens briefly maintain a vigil at Jessica's bedside, waiting for her to wake up and give them a fuller accounting of all of the night's activities. The father of Clare, aka victim #1, faints from exhaustion and stress and is quite sensibly removed to a nearby healthcare facility. Jessica, on the other hand, is left alone and defenseless in the house of murder as the various members of the local constabulary depart in their ongoing pursuit of justice, leaving a sole policeman standing a lonely guard outside the front entrance to the house, where he will be of absolutely no use to anyone. The POV camera of impending doom trails out of her bedroom and up into the still-unsearched attic, where two more victims reside, along with the same cackling figure glimpsed before. As the film ends, the phone starts ringing again, but no one picks it up.
Thanks, Dusty!