There was several of you and he was alone. Why didn't you beat the poop out of him?

But, you decided to take it up to the people in the offices. You certainly made their day. If they take you seriously, that means a lot more work for them, potentially bad rep for the university, blah, blah, blah... The easiest thing for them is to just drop it with "no harm done" mantra. When you've already chosen this route, don't stop and continue to pester them demanding action.

Next time, beat the poop out of him.