When is your lease up?
If soon, I would just start looking for another place. Since you are white knighting someone that doesn't want your help probably best to control what you can control and just leave.
If not soon, I would probably keep calling the cops and not talk to anyone the leasing office again. I would also make sure that when you call the cops you tell dispatch you wish to remain anonymous.
EDIT: I know this is hard to hear (shit it is hard for me to say) DON'T get personally involved. Odds are it will end up physical and even though you will be in the right, when the cops show up it will be two against one.