When the police ask if they can come in, SAY NO. It doesn’t always end as badly as this, but it almost always ends badly.
When the police (or investigators from a regulatory agency, or any enforcement types) ask you questions, SAY NOTHING. You don’t have to talk to them, and it can end badly.
If the cops are getting physical, DON’T FIGHT THEM. You will always lose, and it’s just something else to charge you with.
Not blaming the victim here, but don’t let it happen to you.
For more useful advice — for law-abiding citizens just as much if not more than others — see this fine video called 10 Rules for Dealing with Police:
Credit goes to the partner, btw, who’s probably looking at a helluva lot of harassment for breaking the wall of silence. Breaking the golden rule that Thou Shalt Not Speak Ill Of Another Cop is not a career-advancing move.