They can’t be traced in any meaningful way. That’s part of the point of them. If you’ve had ownership of a coin you can do a bit of tracing, but not that much, and anybody who hasn’t owned the coin can’t trace anything.
Well, except the NSA. If you think government cannot trace bitcoin you are naive.
That is completely untrue.
Every transaction is written on a public ledger that everyone can see. If you are a criminal, the best route is still good ole $20 bills.