According to Foresight News, Craig Timm, a senior director at the Association of Certified Anti-Money Laundering Specialists (ACAMS), stated that the US Department of Justice (DOJ) seems to believe the issue lies with the Tornado Cash user interface, rather than the smart contracts themselves. It appears that without the user interface, charges would be unlikely to be brought forward. The DOJ is attempting to argue that Tornado Cash is not decentralized, but rather a centralized entity operating a website and trying to profit from the services provided.
Additionally, the native TORN token of Tornado Cash is another complicating factor. According to the indictment, the defendants used the token to profit from the operation of Tornado Cash services. The document cites messages they sent to each other and discussions about the necessity of raising the TORN price.