Yes, nowadays its being used in crime, they buy and sell online and pay by bitcoin. Because its untraceable. So police cant get clue to caught them. I think its dangerous.
Even before it is in crime especially in the deep web. Some sites there are operating or have a membership fee the bitcoin. If you pay you can have access to the porn sites there and take note not just a porn site but children there are being abused and rape. Eversince it is used in the illegal transactions like buying of drugs, illegal guns and many more. Bitcoin is used as a currency there and a payment. Some people used bitcoin to transact or hired a killer or hacker there. Bitcoin has a lots of used in the dark net