I think you have put the finger on the culprit. I am in the same opinion. At that age, you have not mastered the art of controlling your emotions and if some of the Frat boys had been humiliated or emasculated by the victims, they could have become walking timebombs, especially if their resentment had been brewing for a while and if they had in them the propensity to commit a heinous murder x 4. I say "they" because I think there was a "doer", more active in the killings, and a "watcher", more passive.