There is no Statute of Limitations on Civil Tax Fraud Prosecutions, only Criminal Prosecution.
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All they had to do is what Weissman did to Trump Campaign personnel in the Get Trump Op.
In a secret proceeding, they requested the Judge pause the statute of limitations on Manafort, who worked for previous administrations, and the Judge did.
On of the charges they brought against Manafort was FARA violations. Hunter was advised to register by an Attorney friend, and Hunter told him that he didn’t understand, he was free to operate without registering.
It’s the other way around. There is a six-year statute of limitations to civilly assess taxes under the 25% omission rule, but no statute of limitations for criminal evasion, which certainly appears to be present here.
That’s the way it was when I worked for the IRS in the 70’s and 80’s. I’m pretty sure the law hasn’t changed since then.