I just can't make any sense of the surviving roommate's story.
Starting with the crying-- who was crying? Who was saying "it will be ok I'm here to help"? I can't make any of this make sense in my mind. If he was leaving and the murder already happened, who would have been crying? Even if one of the girls wasn't all the way dead yet, I can't imagine qualifying the noise they were making as crying. I'd imagine there'd be screaming, yelling, etc. to the point you'd realize something was horribly wrong and you needed to call the cops.
Which brings me to the next question, how do you not call the cops? I'm trying to put myself back into college-- middle of the night, still probably a little drunk, etc. But if you were "paralyzed by fear" you knew this person had been there doing something bad. The "paralyzed by fear" part would seem to eliminate any idea that she just thought it was a houseguest of some sort leaving. I just can't imagine going back to bed.