WASHINGTON (AP) — When a Kansas strip-mall bank with possible mob ties folded in the mid-1980s, federal authorities investigated whether a shareholder, Iranian-born aviation magnate Farhad Azima, should face criminal charges.

The probe hit a dead end. Azima, a U.S. citizen, essentially had a get-out-of-jail-free card because of secretive work he had performed for the U.S. government, a former federal prosecutor involved in the case said. Azima, a gunrunner later tied to the CIA, was never prosecuted.

If he's enjoyed a loose, informal immunity for years, it is now being tested as authorities in...