I mean, honestly, which do you think in the real world is more likely:
1. That a college girl with no history of violence or psychiatric problems was really a closet satanist who was able to convince not one, but two different guys who didn't like each other very much to help her lesbian rape her roommate and then kill her in order to satisfy hidden lesbian BDSM cravings while making an offering to Satan.
2. That her rough trade fuck buddy came over to her place for a booty call, found out that Amanda was out fucking her boyfriend and tried to fuck her roommate and when the roommate said "no" he raped her, panicked and killed her.