Recently, I heard report on national TV.
Police find some drug dealers and had interview with journalists.
They explained that it was very difficult to discover them because they bought drugs in the dark web and paid with bitcoin.
So, it's obvious that bitcoin is perfect tool for criminals.
No names, no bank or government control, it's very easy to exchange bitcoin to local currency etc.
I guess, it's the same for terrorists.
I don't know how to solve it.