But then, what is the proportion of the criminals who use Bitcoin, when compared to those who use fiat currency? As far as I know, the vast majority of the criminals prefer payments in fiat currency rather than in Bitcoin. The reason is that physical cash is much more anonymous than BTC.
Do not tell me from Russia and we only have time to catch for the crime where bitcoin is involved, a lot of police officers were imprisoned, they were noticed for money laundering or drug trafficking brought from Kazakhstan. Here in Siberia, drugs are sold through telegrams for bitcoin, and I also heard that drug addicts get paid in bitcoin.
I don't know how true this is. Here in Singapore, drug trafficking is quite rare. And even with such a low prevalence, most of the transactions are being done in exchange for fiat currency.