Apparently the actual answer (I did say I'm not a lawyer!) is "it depends".

https://en.wikipedia.org/wiki/Possession_of_stolen_goods

The state-level standard appears to vary, the most common case is 'should have known', rather than 'knew for a fact'.

With Bitcoin, where all transactions are a matter of public record, I'd hazard that 'should have known' is baked-in. It will be interesting to see what case law is established in this arena.

That said, my statement above is clearly stronger than reality, except in some states where knowledge doesn't need to be proven.