Although, there are some articles that i have read regarding criminals cannot hide behind bitcoins, still, there are difficulties tracing transactions using cryptocurrencies. That is why law enforcement agencies should have a to change their procedures to pursue criminals who make use of the latest technology to commit crimes. Let the law find a way to evolve to address new tech challenges. There is no reason to expect that law enforcement won’t be able to get a handle on this new cybercrime.
Every advancement has it's Pros and Cons. For Crypto transactions to be excluded from "some" of the cons and be secured by any law enforcement agencies, it should be widely adopted and exposed it's vulnerability meaning share transaction records with the Government like the centralized FIAT's so that they could create and pass some sort of a transparency law and i really don't think if we all want that.