Think about it. Girl and her friend arrive at the dance, the camp, deserted town, whatever. Killer takes them out one-by-one. Ninety minutes later, the sun comes up and survivor girl sits in the ambulance watching her friends' bodies being wheeled past.
Gotta remember that the whodunit may not be as important in our story... You need to figure that it's a horror story, that someone might die at every turn. You have to care if the smokin' hot lit teacher seems a little too interested in his female students. You have to care if the team wins the big game. You have to care if the smart, pretty girl forgives the dumb jock.
