Even if they don't control it, wouldn't a heavy user be able to build a probabilistic model of where the coins went? If you are 99% of the volume on a tumbler,

Even if they don't control it, wouldn't a heavy user be able to build a probabilistic model of where the coins went? If you are 99% of the volume on a tumbler, you know with near certainty that your adversary's coins are being swapped with your own. Paying tumbler fees or even making massive amounts of small-loss bets on a gambling site is well within the resources of a state actor. Bitcoin is small. Eventually real money has to be taken in or out of the system, which gives them a smaller set of individuals to target for investigation.