“It did concern me,” he said.

“But not enough to stop you?”

“I did have doubts about that and then resigned from my bank several years ago.”

“But that was after the fact.”

“Yes, Your Honor.”

Zloch noted that the defendant agreed to “render…substantial assistance to the government” in exchange for punishment that is less than what is stipulated in the sentencing guidelines. But he made sure that Birkenfeld understood that this was no free pass and that any reduction in sentencing would be decided by the U.S. Attorney’s office based on the degree of Birkenfeld’s cooperation.

Birkenfeld was hurried out of the courtroom, looking like a bloated, tan version of Jim Cramer, if the Mad Money host had lost his manic energy. His deep-blue eyes were fixed on the rain outside. If there was one look on his otherwise blank face, it was bafflement: How did Brad Birkenfeld, international banker, end up here? And how could one man inside a huge bank come to threaten a way of doing private-banking business that dates back to Louis XIV?

The last thing UBS needed this summer was Brad Birkenfeld. The public disclosure of his actions, which were later luridly described to federal investigators, was one of several crises to hit UBS this year. It had already written down $38 billion from subprime-­mortgage-related losses, and in the summer it became the target of lawsuits brought by a host of state attorneys general over its role in the auction-rate securities market, which involved investments that were supposed to be safe and liquid for mainstream investors but turned out to be neither. (Those suits have since been settled, with UBS admitting no wrongdoing.)

Yet none of that was as hurtful to UBS and its reputation as the mess uncorked by Birkenfeld. For three centuries, Swiss banking has meant private banking—secretive, exclusive, rich. It has helped make tiny Switzerland a giant in global banking and UBS the largest private banker on the planet, with nearly $3 trillion invested on behalf of its clients.

The damage Birkenfeld caused stems from his lifting the veil of that James Bond-like business to show it for what it is: an often seedy exercise in helping very rich Americans hide their money from the Internal Revenue Service. It now seems more Sopranos than Casino Royale.

Birkenfeld used his deposition to lay the blame on UBS and paint himself as a largely unwitting participant in its schemes. He provided investigators with information about prospecting trips by UBS bankers to events like a yacht race in Newport, Rhode Island, and meetings and cocktail parties at Art Basel Miami, an annual art fair that is a magnet for the globally rich. He said the purpose of these visits was to persuade U.S. citizens to move their millions to undeclared accounts offshore and that UBS not only paid for the trips but also helped people establish sham foreign entities everywhere from Liechtenstein to Panama that existed solely to hide assets from U.S. tax authorities. A UBS spokeswoman declined to comment on any of Birkenfeld’s allegations.

The Securities and Exchange Commission and the Department of Justice seized on Birkenfeld’s deposition and launched separate investigations into UBS in May. The S.E.C. is looking at the bankers who went to Newport, Miami, and elsewhere in the U.S. to solicit business without proper broker-dealer licenses. The Justice Department is focused on whether UBS actively and knowingly helped U.S. citizens evade taxes by creating shell companies that disguised the true beneficiaries.