[toss1]

As much as I'm inclined to agree in theory, the in practice part was settled by SCOTUS in 1927.

Also, if it's any comfort, they wouldn't need to bother with your tax returns. Unexplained deposits and expenditures are often used to convict people of various crimes. So, I'd expect it to be quite an exception for them to bother with upsetting the IRS <-> criminal taxpayer equilibrium.

Hell, it seems pretty routine now for police, TSA, etc. to just find cash and seize it, forcing the owner to defend the legitimacy of the cash in court, as in funding the prosecution of "$12,345.67 vs State of Texas"; yup, you aren't even considered a party, the govt case is setup to be vs the cash pile itself, presumed to be guilty of being illegal proceeds.

Fun Stuff!