> if I knew the serial number of the specific hundred dollar bill provided by the OFAC-sanctioned individual, and didn't spend that exact piece of paper, but just kept it in my wallet, then somehow that makes all the difference and now I haven't broken the law?
If it's in your wallet you've broken the law. If it magically appeared on your doorstep and you call the FBI, you should be fine. (You'll be investigated.)
Anyone who ever sent to or received from Tornado any funds should be talking to counsel.
Doesn't seem to matter whether I spent the hundred dollar bill with the specific serial number provided by an OFAC-sanctioned individual, or if I kept that serial number in my wallet and spent a different piece of paper, since currency is fungible.
By analogy, there's no practical difference between a balance in an Ethereum address getting dusted with tainted funds, or a Bitcoin address with a tainted UTXO that I don't touch.
If it's in your wallet you've broken the law. If it magically appeared on your doorstep and you call the FBI, you should be fine. (You'll be investigated.)
Anyone who ever sent to or received from Tornado any funds should be talking to counsel.