They've got his emails saying he knew money launder happened & he let it happen. If Roman Storm took decisions which showed he's tried to stop it he could've said it in court in defence. He's going to have a difficult time in court.
In that case, I'm interested to see what will be ruled. If the basis is that he knew ML was happening though didn't stop it, I think it will be argued that it is impossible to pick and choose certain transactions from interacting with a smart contract/decentralized and non-custodial protocol, and a complex job (technically) to identify or add any kind of measure to prevent it (any faster than how fast they sanctioned Tornado Cash to begin with).
"Letting it happen" means that it's something that can be controlled. A decentralized protocol like TornadoCash is not administered even by Roman. Yes, he's a developer, and has the most know-how around the code, but it's still decentralized. He couldn't just turn it off, make appropriate changes and turn it back on. As well as that, developing functions that would filter or deter money laundering is not a simple thing to make
on-the-fly (as even
to this daytoday, AML scores are subjective and not sure-fire ways to detect money laundering). With this in mind, it might not be as difficult as it seems to defend himself.