Nishi isn't stupid, and he did seem annoyed. So personally, I don't think so.
I have the impression that nishi was bored and that was why he left his classmates throw him out of the window, i don't remember any reaction or any gesture of disgust from Nishi, so he was just there... waiting for a reason to kill them
Because attacking the police would draw unnecessary attention, just like slaughtering his colleagues, but worse. And presumably running away is a bit difficult, otherwise surely he would do so.
btw: if Nishi is to be caught by the cops, who called them? and why isn't he running or attackin? he is about to take on about 30 guys with his bare hands!! can't he take on a couple of police officers?! or just run away like Kurono did in his solo mission?? :confused: