[alec]

Since the Bitcoin blockchain is public, couldn't you follow the money? Make a list of all wallets that accepted these funds initially, and then do graph analysis, either to see where the money went or provide others with a tool to avoid transactions with those wallets?

[sltkr]

Yes, but this is somewhat like saying you could mark the banknotes used to pay off a person that's blackmailing you. If you catch someone with a marked note that doesn't prove they are the perpetrator; it just means that they received your money somehow.

[Phlarp]

Theoretically yes, but in practice mixing services make this much much more complex.

[Karunamon]

Problem is that doesn't really help you identify the perpetrators. Both mixing services, and the fact that a user can generate unlimited wallets (if someone sends money to a wallet, you can't prove they own the second wallet or if they transferred money to someone else) makes this very difficult.