Bradley Birkenfeld was released from federal prison in August 2012 after serving 2½ years for his role as a Swiss banker hiding millions of dollars for wealthy American clients.

Five weeks later, he found himself in the kitchen of a small rental house in Raymond, New Hampshire. At that moment, Birkenfeld was an ex-con. He was out of work, infamous in a famously discreet profession, and probably unemployable as a private banker anywhere.

But then his lawyer walked into the room, carrying a check from the U.S. Treasury to Birkenfeld for $104 million—minus taxes. On the face was a picture of the Statue of Liberty.

It was Birkenfeld's cut as a whistleblower of the massive settlement his former employer—the Swiss bank UBS—had paid to the United States government in a settlement for helping Americans dodge taxes. As Birkenfeld signed the check, he was transformed from convicted felon to government-made multimillionaire.

"It was vindication," Birkenfeld said. "I am glowing. I love it."

"It was vindication. I am glowing. I love it."

Today, Birkenfeld has a new rental house by the ocean in New Hampshire, two Porsches, and a collection of pricy vintage hockey gear to display in his own Boston Bruins luxury box. He's made charitable contributions in his community. And he's planning to open a sports museum.

You'd think he'd be happy.

But Birkenfeld, 50, a big man with a brash style and a temper, isn't done with the U.S. Department of Justice. He's on a quest, he said, to force the government to explain why it was so aggressive in prosecuting him, but let nearly everyone else involved in the scam get off with light penalties or none at all.

Now Birkenfeld is telling his story exclusively to CNBC. Wealthy, out of prison and soon to be removed from federal probation, he says he's now free to explain how he came to be the man who ended the tradition of bank secrecy and got rich in the process.

The reverberations from Birkenfeld's disclosures have been titanic, playing out on a global stage. The United States forced UBS in 2009 to pay a $780 million penalty and admit it conspired to defraud the United States by impeding the IRS from obtaining information on American taxpayers hiding money in Switzerland. In 2014, banking giant Credit Suisse pleaded guilty and said it would pay $2.6 billion in penalties. American investigators soon followed the trail of hidden money to banks in Israel, India and around the world.

During this time, the IRS offered a series of compliance programs designed to lure Americans to confess their secret offshore accounts and pay hefty penalties in exchange for a promise they would not be sent to jail. Some 50,000 Americans have taken the IRS up on that offer, pouring $7 billion into U.S. Treasury coffers.

Shocked by just how rampant offshore tax dodging was, Congress passed a law in 2010 designed to force banks around the world to disclose accounts held by Americans to the IRS. For the first time ever, banks affected by the law must begin disclosing that information to the U.S. government this year.

It has gotten much harder to hide money in secret foreign bank accounts, the insiders say. Soon it may be nearly impossible. And the experts give a large part of the credit to Birkenfeld.

"We're on the verge of an environment where offshore bank secrecy is essentially dead," said Scott Michel, an attorney with the law firm Caplin & Drysdale in Washington, D.C. His firm has represented more than 1,000 American clients who have disclosed secret accounts to the government in the wake of Birkenfeld's disclosures.

"I think the game is over," Michel said.

But the whistleblower himself doesn't think the U.S. government has gone nearly far enough.

Why did the Department of Justice not press the Swiss banks for the names of all of the Americans who had secret accounts there? Why did the IRS design a compliance program that allowed 50,000 Americans to admit they broke the law but remain safely anonymous, protected from embarrassment of admitting guilt?

To Birkenfeld, all this is evidence that the U.S. government is still enabling the wealthy and powerful Americans who hid their fortunes in Switzerland: CEOs, movie stars and even American political figures. It's one of the great mysteries of the entire saga: Out of the tens of thousands of Americans who hid money overseas, the government has only indicted or charged a relative handful. Only a few have gone to jail.

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While Birkenfeld is talking to CNBC, he is still holding information close to the vest. He will not name the clients who he turned over to the government. Of the 30 names he says he gave the U.S. government, only one has been charged and publicly named, he said.

The Justice Department declined to answer specific questions submitted by CNBC.

Birkenfeld is not the only one criticizing the Justice Department. A damning 2014 report by the Senate's Permanent Subcommittee on Investigations criticized the department for failing to even obtain the names of Americans who had secret accounts, despite the extensive legal wrangling with UBS and other banks.

The report found that of the 22,000 Americans who had Swiss accounts at Credit Suisse, the U.S. government got the names of only about 230 clients. The Justice Department, the report found, "did not use any of the authorities and remedies available to it in U.S. courts … to obtain U.S. client names and account information directly from Credit Suisse."

There is probably no one angrier about all of that than Birkenfeld. Sitting in his luxury box at the Boston Garden as his beloved Bruins got set to play the Buffalo Sabres, Birkenfeld reflected on his own personality, and why he's coming forward now, when many others would be happy to spend their millions in a luxury retirement.

"I'm a hammer looking for nails," Birkenfeld said. "A chainsaw looking for trees. The worst person they could ever p---off? Me. Because I'm relentless and I'm resourceful and I will get the job done."

A big part of Birkenfeld's joy, he said, is his feeling of schadenfreude over the pain he believes the massive payout caused his antagonists inside the U.S. government. "Oh, they were p---ed," Birkenfeld said, with a grin. "And I'm pleased."

One more thing: Birkenfeld got $104 million. But he and his lawyers are working to get more money.

Maybe quite a lot more.

From Boston to Geneva

Birkenfeld was born in Brookline, Massaschusetts, just outside of Boston in 1965, the youngest of three boys of a neurosurgeon father.

He fell into the finance industry as a summer intern at State Street Bank in Boston, ultimately working as a trader for institutional pension plans.

It was there that Birkenfeld said he had his first brush with whistleblowing. Birkenfeld said he discovered irregularities in the procedures at the bank. "It was first errors, and then, knowingly, committing a cover-up of that, which is fraud," Birkenfeld said. He began to keep copies of relevant documents at home, as well as at work. "The problem was that they weren't willing to admit fault."

Executives at the bank, though, were able to find fault in Birkenfeld: They put him on probation, and then fired him, Birkenfeld said. He added that executives began circulating critical stories about him.

A spokeswoman for State Street confirmed Birkenfeld's employment at the firm, but was unable to substantiate his account of events decades ago.

Next, Birkenfeld said he went to the FBI with what he knew. But he found the FBI agents didn't have a grasp of the intricacies of banking. "They were totally clueless," he said.

Frustrated, Birkenfeld headed to Switzerland.

He got an MBA at the American Graduate School of Business alongside Lake Geneva in La Tour-de-Peilz, Switzerland, and then began to look for work.

His first stop was Credit Suisse, then a couple of years later to Barclays where, for the first time, he worked directly with clients.

One of the clients he made contact with was billionaire American real estate developer Igor Olenicoff. When Birkenfeld switched jobs again, to UBS, Olenicoff, and what became a $200 million account, came with him. Birkenfeld's mission at UBS was business development for the United States. UBS wanted rich Americans as clients, and Birkenfeld was one of a team of bankers sent to lure them in. He became one of the very few Americans admitted to the inner sanctum of Swiss bank secrecy. Olenicoff pleaded guilty to a count of filing a false tax return, admitting tax evasion and paying a $52 million penalty

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Olenicoff declined to comment through his lawyer.

Birkenfeld said he began to see clients coming into the bank with a million dollars in a suitcase. Specialized couriers bringing cash into Switzerland and turning it over to the bank's clients for deposit. He learned that $10,000 in bills was exactly a quarter-of-an-inch thick. And he learned that the best banknote for cash transactions was the 1,000 Swiss franc bill. "The largest note in the world," Birkenfeld said. "I mean, you could put a half a million dollars in your pocket, no problem."

They didn't ask too many questions about where the money came from. "It wasn't our business to know," Birkenfeld said. "We weren't policemen. We were bankers." He noticed that many clients tore up receipts of deposit on the spot.

It's not illegal for Americans to have bank accounts in Switzerland. But under the law, taxpayers must disclose all foreign accounts and pay tax on any earnings in them. Similarly, bankers must be registered with the SEC in the United States before providing investment advice here.

Inside UBS in Switzerland, though, thousands of American clients were ignoring the tax rules and scores of bankers were traveling back and forth to the U.S. to recruit clients without ever registering with the SEC.

UBS put an enormous effort into identifying and cozying up to the richest people in America. The firm targeted families with inherited wealth, entrepreneurs who'd cashed out of businesses, and even professionals with modest wealth such as doctors, architects and lawyers. To reach them all, UBS bankers hit the social circuit. UBS strove to put on the best events in the world and lure in billionaires: art festivals, music venues, yachting events. Former UBS employees say much of it was organized by a charismatic and smiling colleague they nicknamed "Captain Cocktail."

CNBC contacted several former UBS bankers and executives in Switzerland, as well as former consultants and advisors outside the bank. A number of them spoke candidly, if privately, about life inside the ultra-discreet world of Swiss banking.

"This (article) concerns a legacy issue for UBS that has been well documented and is many years behind the firm. UBS fully and finally resolved all of our U.S. cross border issues in November 2010," said a UBS spokeswoman. "The business described has been closed since July 2008. UBS today is a different firm, with a different strategic focus and senior management team,," she continued. "Mr. Birkenfeld was convicted for aiding and abetting tax fraud and for lying to U.S. authorities about his own misconduct. Following 40 months of prison for conspiracy, he remains on supervised leave to this day."

UBS knew the billionaires had a lot of choices—invitations to anything and everything. They strove to make their events stand out. One easy way to do that: parties often had "two women for each gentleman," recalls one event attendee.

UBS's private wealth team wanted to forge an emotional connection to the clients, say former employees. The goal was to spend a week with a billionaire in St. Barths, and to be the only banker on the yacht. Don't worry about meeting the client at 9 a.m. in his office, but pin him down at 8 p.m. at Carnegie Hall.

One tactic that worked especially well, the event attendee said, was seeking out the oldest women in the room, charming them, and then asking for introductions to all the billionaires at the event.

As dazzling as the social swirl was, the day-to-day reality of Swiss banking in Zurich and Geneva could be grimly competitive for the rank and file.

Many bankers inside the secretive private wealth management unit arrived at their desks by 7 a.m., only to find a worksheet on their desks detailing the previous day's profits and losses. It listed every banker's results by name. "You had a hit parade that showed this guy was No. 1, this guy was No. 2, and this guy was No. 35," recalls one former banker. "Imagine what type of climate that was to work in."

The Swiss bankers saw themselves as carrying out a solemn duty to protect their clients' identities. For many, it was a point of pride: "Every client was treated the same," says one. "Numbered accounts, named accounts, they were under the same secrecy."

The bankers were given elaborate instructions on maintaining client privacy. To some of the bankers, it began to feel as if they were becoming undercover agents. Birkenfeld provided CNBC with a document he said was handed to bankers in the private wealth division during a training session, in order to role play various scenarios they might encounter as they traveled to the U.S. to recruit clients. The paper encourages UBS bankers to mail sensitive account documents ahead of time to trusted contacts so not to be caught carrying them through U.S. customs. It suggests they should not detail client names in their electronic devices, and to only note "very short remarks" about the topics for any meetings with American clients.

According to one former UBS banker, managers gave the private-wealth team specially encrypted laptops that could be easily deleted in case U.S. authorities barged in. "They told us about the computers, 'if ever you run into problems in the U.S. with the IRS, just push button X twice, and everything will be deleted,' " said the banker. "It was like James Bond."

But the elaborate efforts to keep the U.S. government in the dark began to worry the bankers. "When these computers came along, some of the people realized, 'My God, what we are doing may actually be illegal,' " the banker said. "We never were instructed on American law and what was allowed. We never had any lessons."

Also worrisome to some of the UBS employees were the identities of the American lawbreakers they were protecting: names that still have not been made public despite years of investigations.

"There are some very big names, and it would shock the establishment," said a former UBS insider. "Movie stars, upper East Coast establishment figures, people who trace their origins to the '20s, '30s and '40s. They're the walking history of the American economy."

Beyond that, Birkenfeld said there was an even more secret category of client: American political figures.

Under international banking law, banks are required to treat their political customers with a higher degree of scrutiny in an effort to root out international corruption. One set of international guidelines sets aside a separate category of client, known as a "politically exposed person," or PEP. They are defined as heads of state, heads of government ministries, senior judicial officials, high-ranking military officers, as well as senior officials of political parties and their close associates and families.

Birkenfeld said UBS had a specific banking desk to deal with PEP clients, and that desk had an American division. "It was another level of secrecy," Birkenfeld said. He does not know the names of any American political figures who had secret accounts in Switzerland, or how many there were, because he did not work on the desk. But he said it was widely discussed inside the bank: "My bosses used to tell us, 'If you ever have a PEP it goes to the PEP desk in Zurich,' " Birkenfeld said.

Other former UBS insiders back up Birkenfeld's account of politically connected Americans inside the bank.

"The so-called PEP clients? That's definitely true," said one.

"They existed, yeah," said another.

Birkenfeld said that he has given the names of all of the American clients he has—30 people—to the U.S. government. But, he said only one has been named publicly, and none have gone to jail.

According to a document compiled in 2013 by the legal team working for Beanie Baby billionaire Ty Warner—one of the few Swiss bank clients whose name has been made public—just under 50 American clients of offshore banks have been sentenced in the U.S. since the Birkenfeld revelations. One received a 19-month sentence. But Warner's team found that nearly 30 were given punishments that included no jail time at all. In the end, Warner was also sentenced to probation without jail time.

Birkenfeld served more time in prison than any of them.

'I'll Take You Outside Right Now.'

The beginning of the end came for Birkenfeld at UBS after a colleague alerted him to a document posted to an internal server that set new procedures for private bankers, Birkenfeld said. The document, which was not called to his attention or mentioned in training, was a set of guidelines for bankers that instructed them to do exactly the opposite of what their bosses were telling them to do every day, he added.

He began to suspect that he and the other bankers were being set up. If any of the Swiss bankers were caught in the United States, Birkenfeld suspected UBS would point to its internal policies and simply label them "rogue" bankers. He carefully printed off a copy of the document and took it home. Then he confronted his boss.

"I grabbed him by the shirt and I said, 'I want an answer to this. This is bulls---. You're putting this document out here and you're not giving me and my colleagues an answer."

Birkenfeld said his boss told him not to rock the boat.

"I said: 'I'll take you outside right now. I'll get in a fight with you over this. I'm p---ed off. Because you're now lying to us. And you've put us in harm's way.' "

After that, Birkenfeld said he began to copy and hide UBS documents in Switzerland, France and the United States. Then he resigned and hired a lawyer. After a legal battle with the bank over his bonus, Birkenfeld began making overtures to the IRS, the SEC, the Senate and the Department of Justice.

But there was no relief. Birkenfeld went almost directly from fighting with his Swiss bosses to fighting with the U.S. government.

Almost from the start, Birkenfeld's relationship with the Department of Justice was fraught with tension, beginning with a dispute over whether he was officially a whistleblower or just a "tipster," as one Department of Justice official referred to him. Birkenfeld felt the department did not move aggressively.

"I coulda done their job," Birkenfeld said. "You coulda fired the whole tax division at DOJ. I coulda done this job better, trust me. And I offered to do it."

Birkenfeld said he offered to wear a wire to record conversations with bankers and clients, but the DOJ said no. He said he turned over the names, cellphone numbers and preferred U.S. hotels of UBS bankers in the United States, but the DOJ did not tap any of the phones. He said he offered to come into the DOJ each month to go through the complicated material but was rebuffed. Birkenfeld grew frustrated and angry at the prosecutors he was working with.

"Oh, OK, fine. Just go eat another jelly doughnut," Birkenfeld said. "It's a prerequisite to be incompetent to work there. I'm telling you."

At the same time, prosecutors inside the department were coming to the conclusion that Birkenfeld was not being entirely straight with them. Soon matters came to a head, with the government accusing him of failing to tell the entire truth about one of his clients, the California billionaire Igor Olenicoff.

On his next flight from Zurich to Boston, Birkenfeld was arrested as he got off the plane at Logan Airport. "I knew I was gonna be arrested," Birkenfeld said. "I couldn't trust the DOJ. I knew that they were hostile."

Birkenfeld pleaded guilty to one count of conspiracy. At the sentencing in a federal court in Florida in 2009, government prosecutor Kevin Downing heaped praise on Birkenfeld, even as he asked the court to sentence him to jail. "I will say that without Mr. Birkenfeld walking into the door of the Department of Justice in the summer of 2007, I doubt as of today that this massive fraud scheme would have been discovered by the United States government," Downing said.

Birkenfeld said he is angry that Downing later left the government and took a job at a law firm where he is defending many of the Americans who had secret accounts. At the time Downing left DOJ, Reuters reported that he "expects to advise companies rather than individuals."

Downing did not respond to a request for comment for this article. The Department of Justice has a variety of ethics guidelines for former employees, and there is no evidence to suggest Downing violated them.

Mister 30 Percent

In prison, Birkenfeld said one of the guards nicknamed him "Mister 30 Percent," because of the prospect that the government might pay him an enormous amount of money. In the end, the IRS calculated Birkenfeld's $104 million payment on the basis of the $780 million that UBS paid the U.S. government. But his lawyers have maintained that he is entitled to more—a percentage of all the money the government has collected from Americans confessing secret offshore accounts.

So far, the IRS said as much as $7 billion has been collected from Americans with secret offshore accounts. That number continues to grow.

It's not clear whether that argument will prevail. The IRS declined to comment for this article.

On its website, the IRS explains that whistleblower rewards are based on "additions to tax, penalties, interest and other amounts collected as a result of any administrative or judicial action resulting from the information provided." The IRS sets a general range of 15 to 30 percent for whistleblower awards. The website said: "There is no limit on the dollar amount of the award."

"If the law is written that way—if the moneys they've collected—I believe there's other proceeds that I should be allocated, yes."

Should he get a billion dollars?

"Again, you'll have to talk to my lawyers on that," Birkenfeld said.

He argues that the billions of dollars returned to the U.S. Treasury are just the beginning; huge sums were also returned to the American banking system as offshore clients returned cash to disclosed bank accounts in the U.S. "You can't possibly calculate the amount of money that's been generated as a result of this historic whistleblowing that I performed," Birkenfeld said.

Birkenfeld is still hiding something: He will not publicly name his own clients at UBS, although he says he provided that information to the government years ago. Pressed by CNBC to reveal the names of his clients, Birkenfeld demurred. "I don't want to give the names at this time," he said. Instead, he suggested that CNBC call the Department of Justice and ask officials there for the names.

The department, though, has little to say on the topic of Birkenfeld.

A spokeswoman declined to answer a series of direct questions from CNBC about his case, instead providing a statement from Acting Assistant Attorney General Caroline D. Ciraolo of the Justice Department's Tax Division: "Bradley Birkenfeld was afforded due process of law and sentenced by a federal district court after full consideration of all relevant facts and circumstances, including his admission that he advised wealthy UBS clients on how to conceal their assets from the U.S. government," she said.

The Justice Department went on to point out that since 2009, the department has charged more than 100 account holders with undeclared offshore accounts, dozens of facilitators, and financial institutions. "The department's enforcement efforts have reached far beyond Switzerland, as evidenced by publicly disclosed actions concerning banking activities in India, Luxembourg, Liechtenstein, Israel and the Caribbean," DOJ said in a statement. "The department continues to work with the Internal Revenue Service and other domestic and international law enforcement partners to aggressively pursue those who assist U.S. taxpayers in offshore tax evasion and to identify the individuals who have evaded their federal tax obligations."

As for Birkenfeld himself, he won't be staying in the United States for long.

Birkenfeld said that he will leave the U.S. once his probation is over in November. He'd like to renew his dream of living in Europe, although he knows he may never set foot in Switzerland. He may relocate to Germany.

In the meantime, he talks with his lawyers, connects with other whistleblowers around the world and makes charitable contributions. He has looked into getting a presidential pardon. And he says he's working on a book.

Birkenfeld is also enjoying the fruits of his whistleblowing.

The vanity license plate on one of his two new Porsches bears the old marketing slogan for UBS: "You and Us."