Bradley Birkenfeld once lived the high life as secret Swiss banker at UBS in Geneva. Then he delivered some of the world’s best-kept secrets to the US government, expecting a great reward. And now he sits in federal prison in Pennsylvania.

How’d that happen? It began in 2007, when the American-born Birkenfeld approached the Department of Justice with surprising evidence that UBS was helping alleged American tax cheats hide assets in Switzerland's famous secret banking system.

He told the US government that 19,000 American clients had about $19 billion dollars of assets at UBS.

"I'm going out of my way,” he said in a prison interview. “Risking my career. Risking my reputation. Risking my life. And trying to unfold the largest fraud in US history."