A crypto-mixing service, or a cryptocurrency tumbler, tries to hide the original source of potentially identifiable cryptocurrency by combining it up with other funds in a single pool. The cryptocurrency is lumped together with funds from other sources and then redistributed at random to the destination address. This practice makes it incredibly difficult to track cryptocurrencies such as bitcoin, but law enforcement investigations that result in the seizure the records of cryptocurrency mixers can provide information that could potentially unmask the criminal operators responsible for transactions. Even though it is difficult to investigate cyber-crimes, it is still worthwhile to report criminal activity to federal law enforcement because this information is necessary to start investigations that can eventually lead to enforcement wins such as this case.

https://www.justice.gov/opa/pr/ohio-resident-pleads-guilty-operating-darknet-based-bitcoin-mixer-laundered-over-300-million