"Exclusive: Mueller Enlists the IRS for His Trump-Russia Investigation"
"his probe has enlisted the help of agents from the IRS’ Criminal Investigations unit.
This unit—known as CI—is one of the federal government’s most tight-knit, specialized, and secretive investigative entities. Its 2,500 agents focus exclusively on financial crime, including tax evasion and money laundering."
http://www.thedailybeast.com/exclusive-mueller-enlists-the-irs-for-his-trump-russia-investigation
It's all just rumor from sources at this point. The idea that Trump might get RICO'd does warm my heart...