Bitcoin transactions can be easily tracked down and most Bitcoin mixers (if not all major of them) are either controlled or directly set up by national security services.
Yes I would not be surprised to learn that Bitcoin mixers were controlled or at least heavily monitored by government agencies.
Hiding large sums of anonymous money would be the type of thing that would certainly get attention from the three letter agencies as we call them in the US.
(DEA, CIA, FBI, NSA, etc)