Bitcoin and other cryptocurrencies undoubtedly offer new opportunities for financial transactions. However, they can also be used for purposes of financial crime, such as fraud and money laundering. The absence of central control and the pseudonymous nature of transactions make cryptocurrencies appealing for illicit activities.
Let us not be too focused on bitcoin or cryptocurrency in general, financial crime has always existed between the financial institutions, governments and some individuals and this has always been the norms, it has been happening and keep repeatedly happening, government cannot control it, why would having financial control be more effective on a decentralized network with thebuse of AML agencies when they aren't done yet with fiat, those using it for illicit activities are less of our concerns as long as we know the best means to stay off their limit from attacking us.
What do you think can be done to mitigate the risk of cryptocurrencies being used for criminal purposes? What measures should be taken?

Nothing, we just have to leave it as it is, all you could do is to know how you could safeguard your own asset and get secured, if you're not been vulnerable, they won't attack or scam you successfully, make use of a decentralized wallet and don't expose your personal details.