This was the first thing I thought of. Why the heck would the admins read random notes sent by users? Obviously there is the potential for abuse for this kind of service, so from a liability perspective you'd be better of deliberately ignoring all messages.
Or rather, even if the admins were knowingly facilitating crime, from a liability perspective they would be better off reporting/rejecting any users that say they're committing a crime and only do business with criminals smart enough to wink wink nudge nudge.
I can only think of two scenarios where someone would tell a mixer the money is dirty:
1. They are law enforcement
2. They have already been caught by law enforcement and are being used as bait, either knowingly or not
Or, and this is the most likely in my opinion, but it is just a guess. The undercover said they had a lot of illegally sourced coins to mix, asked the Mixer admin to help them mix such a large amount and offered them an additional reward in exchange. That said, we should not jump to any conclusions until evidence is presented. The government could be fronting a strong case in the indictment and then it turns out to be much weaker when presented.
Or rather, even if the admins were knowingly facilitating crime, from a liability perspective they would be better off reporting/rejecting any users that say they're committing a crime and only do business with criminals smart enough to wink wink nudge nudge.
I can only think of two scenarios where someone would tell a mixer the money is dirty:
1. They are law enforcement
2. They have already been caught by law enforcement and are being used as bait, either knowingly or not