What the article does not state, is the very probable possibility that this Banker is being paid huge whistle blower fees for revealing all of the information on his ex bank clients. Those finders fees are large enough to allow the recipients to retire in luxury for the rest of their lives. Turning Americans with assets abroad into the IRS is extremely profitable. See IRS Form 211 for the form used to turn in Taxpayers in exchange for handsome finders fees.
The IRS has special forms for reporting Mexican corporations, Mexican Fideicomiso Property Ownership, Mexican Bank Account and other Mexican Financial Assets which must be filed with your US tax return. Failure to file those forms or filing them late can result in penalties of $10,000 or more and possible criminal prosecution. The "good old days" of not disclosing your income or property in Mexico and disappearing fast.