U.S. tax authorities have awarded $104 million to a former banker at UBS after he told them how the Swiss-based bank help thousands of Americans evade taxes through their overseas accounts.

Lawyers for the whistleblower, Bradley Birkenfeld, announced the award Tuesday. They said it was the largest ever handed out by the U.S. tax agency, the Internal Revenue Service. The IRS confirmed the payment.

Birkenfeld is credited with telling American officials how the bank persuaded rich Americans to open UBS accounts, managed $20 billion of their assets and assisted them in cheating the U.S. government.

The 47-year-old Birkenfeld pleaded guilty to conspiracy in the case, and served 31 months of a 40-month prison sentence before being released early last month with time off for good behavior.

UBS avoided prosecution in the case after it agreed to pay $780 million to the U.S. and turned over information on 4,700 of its accounts held by suspected U.S. tax cheats. Since the Birkenfeld case became known several years ago, at least 33,000 Americans have voluntarily disclosed various offshore accounts to the government and paid $5 billion in back taxes.