Why? What's wrong with law enforcement agencies in those countries? Any criminal activity can't be locked inside blockchain, it always has lots of outer actions. Moreover, Bitcoin's blockchain is transparent so you can trace different criminal transactions once you found connections with a criminal activity. And we can learn from media that police of different countries often uses that option. And we know that some criminals used traditional bank systems for tens of years (and some for sure still do it), so it is not preventing crime activities.