Would have been more interesting if (spoiler)

those freaks turned out to be her best friend and the boyfriend. the randomness of the identities of the killers is certainly chilling because when you think about it, you never really know what another person is thinking or what sick fantasies they're entertaining or simply because you are then confronted with the fact that for some people, killing is FUN. i think it's even creepier, however, to think you know the people close to you, to believe they'd never hurt you and then realizing you were wrong all along. it would have been so twisted if it turned out to be them.