My 2 cents...
First of all, do not try to confront him yourself.
My first step would be to talk to the building manager/supervisor. If nobody is complaining to them, and are only trying to handle it themselves, the management may not even be aware there is a problem.
If the management seems unwilling or unable to do anything, then and only then would I try to get the cops involved.
Well...I went over to the office. The lady there said if there's another disturbance, I can call the on-call maintenance person, who will stop and put a note on their door. Well...that'll help...how?
I'm assuming it would also be annotated somewhere, though. So there's that. But she said there isn't anything they can do about a complaint without being able to verify that I'm telling the truth. I guess that makes sense, though it stings a bit.
Hopefully someone else complains, too. Then I won't sound like a hypersensitive kook.