The Mafia at all levels of the human society exploits all possible means of money laundering, there is no doubt that cryptocurrency are used for this also. Maybe someone will think that's bad, and it is when only a negative aspect is viewed, but it also show that bitcoin and some others coins actually have practical application in today's society. Mafia is also using fiat, gold, silver, real estate business, and any other form of value or business for money laundering.
But compared to all the above, in my opinion percentage of laundered money with cryptocurrency is less then 1%. Let's just take the example of a small branch of
Danske Bank which is laundering 200€ billion, and we can only guess what other big banks do regarding that.