> it still has nothing to do with the feds tracing Monero It has everything to do with the feds tracing monero. You know why they knew he used that exchange? Because they traced his monero to it. If you stop them from tracing the money in the first place, they never learn what exchange he uses, and thus they don't know who to subpoena for user info.

this is exactly right. they were already watching his account in the CEX and saw the monero arrive there. the moral is "don't think that sending your surveiled Bitcoin through a swap to your exchange account makes them clean"