This has not been settled by law. It is one of the weaknesses of BTC. Each USD is basically fungible. You cant tell if your dollars have been used previously in a crime, so each one is worth the same as the next (except in rare exceptions - like where money serial numbers have been logged, or its been tainted with theft ink from a bank robbery or something) This fungibility is backed up by centuries of court cases that have held it up.
Bitcoin has no such protection and its easily tracked to any number of crimes. So it can be a crime to even hold certain bitcoin, and you may not know it, yet.
And now that a huge amount of Mt Gox coin has been stolen, we are all likely fencing a portion of that stolen material every time we trade.