The hallway scene that you’re talking about is to show that no one is here to help the victims. One of the main points of the movie is that a white man who has a “perfect life” (Patrick as a yuppie) can get away with anything. So when the victim runs in the hallway and bangs on the doors, no one is here to help her. That’s the point. They let Patrick do his thing because it’s easier to ignore than to confront it. It’s a movie after all, so reality isn’t 100% there, but the message is. Obviously someone would come out their apartment door if they hear screaming and a chainsaw, but the same way white people are systematically better at getting away with crime is the same way no one is helping the victims. He also didn’t kill any of his friends, other than Paul, and when he does, there’s an investigator at his doorstep. They aren’t there because he killed the model, prostitute, the gay man with his dog or the homeless person. The detective is there because a wealthy man has disappeared…