Until now bitcoin is used for crime or illegal purpose and others are used by druglords, if they buy drugs they pay the bitcoin so they do not get caught by the police, so we need to be alert for everything to avoid.
Let's not forget the fact that fiat is also used illegally. But the truth should be said that BTC lessen the risk to be caught when you use it illegally though it doesn't mean that you can get away with it. Police nowadays should also upgrade since criminals are getting smarter day by day.
If Bitcoin is really privacy, why do the Korean and American government can catch many criminals recently? Internet is a freedom place to using, so, the data transfer through internet all can tracks by anyone, as long as you want to do that and spend much times to find crimial.