The Securities and Exchange Commission petitioned in Federal Court recently to increase the statute of limitations from 5 years to 10 years to better equip themselves for trials, and conduct more thorough investigations in preparation for trial.
They were denied.
I would not be shocked to see arrests by the IRS or the FBI on any scam 4 years and 364 days from the start of the investigation.
Don't forget the failure to pay taxes!!! If you pay the taxes you admit the crime. There is no way out. Why do you think the FEDS have a 99% win ratio.