Bitcoin is only pseudoanonymous. At some point, the 'bad actor' has to access 'legitimate' banking institutions to exchange the Bitcoins to fiat and that is the weakest link. It requires reporting to relevant tax or other authorities based on arbitrary (and secret) amounts, but targets money laundering, drug trade, gamlbing, etc.

I suppose if I had to throw a potentially disruptive idea out there, you could create a database of 'blacklisted addresses.' Let's say when Bitlocker came out, you entered that address into a database and it was verified as being associated with this scam, well it is trivial to track those coins between addresses and every address it enters is blacklisted until it enters a mixer or exchange, at which point you have a potentially complicit corporation that you could actually target with the subpoena or other legal action for discovery of IPs, login, etc.