Explanation for Prof. Callaghan's misguided bloodlust?

But what I didn't get the first time I saw this movie, and every time after; why is/does Professor Callaghan so readily and actively trying to kill his innocent students; whom he had a close relationship with, mentored, and encouraged to do greatness. Particularly his new token favourite, Hiro; the kid who created the weapon he's currently utilising, and that he'd only just permitted entry to his university not too long ago.
I mean, I realise the believed "death" of his daughter drove him to seek vengeance on Alistair Krei, but that had nothing to do with the central characters.