I went so far as to look into the IRS Criminal Investigation manual, and I will admit it was a challenge to take it all in. But I found it quite curious that the IRS were the ones who initiated this investigation. (see page 21 of https://www.justice.gov/usao-n... ) Not much more is said about it, but I have to question why was the IRS investigating a torrent site? Is it because someone running it may have been in the US, and may have been profiting from it? That is the only thing I can think of, but that leads to all kinds of other questions.
Apparently one of the charges against him is money laundering and that falls under the purview of the IRS. Remember, they put Al Capone away for tax evasion.