I'm speculating here, but they probably asked the FBI or some US agency for help tracking crypto transactions. The IRS probably got involved by those agencies w

I'm speculating here, but they probably asked the FBI or some US agency for help tracking crypto transactions. The IRS probably got involved by those agencies with the excuse that people may be hiding income from the illicit transactions... but also because the IRS is, besides maybe the intelligence agencies, one of the agencies with the best crypto-tracking technology and capacity in the US.