Good question, once police knows the household they will check the background on all the occupants and neighbors. If still they can't find anything and they dont feel like wasting time , they will get warrant and confiscate all laptops for forensics but most of the time they can tell just by checking the background who's the culprit.

I would suggest to watch the documentary about the guy who was behind the darkweb site - the silk road.

That's some impressive police work right there.