For more than two decades, prosecutors allege, Swiss financial adviser Josef Beck practiced the dark art of handling dirty money.

He conspired with Switzerland’s biggest bank, UBS Group AG, to help dozens of Americans evade taxes, once using a young child to deliver a bag of cash to a client, according to a 2012 federal indictment (PDF). He has never come to the U.S. to face those charges, and the Department of Justice considers him a fugitive.

Yet in a low-rise Zurich office building, the Beck family business of advising wealthy Americans lives on.

Just a few weeks after his indictment, Beck’s directors formed another company to manage money for American citizens, records show. This new entity is owned by two of Beck’s sons and shares an office, staff and a board member with Beck’s firm. A company brochure describes the two companies as being under “common control.” And it’s likely that Beck’s U.S. customers moved to his sons’ firm, according to an attorney representing both companies. The attorney said the two firms operate separately and that Josef Beck, who still runs his own company, no longer advises American clients.

Beck’s staying power shows how hard it can be for U.S. authorities to crack down on suspected international financial crimes. He’s one of dozens of foreigners -- including Swiss bankers and Argentine soccer marketing executives -- the U.S. has charged in recent years with wrongdoing allegedly committed overseas.

“The overlapping relationships and the nature of the business are such that they raise suspicion about Mr. Beck’s continued involvement” in the company that advises American clients, said Jacob S. Frenkel, a former official at the U.S. Securities and Exchange Commission and now a partner at Shulman Rogers Gandal Pordy & Ecker. “If I were putting my government enforcement hat back on, I would be all over this, wanting to know more.”Broad Probe

The sons’ firm registered with the SEC as an investment adviser shortly after Beck’s indictment in March 2012. The SEC isn’t permitted to disqualify a registered investment adviser because of an indictment, so Beck himself could legally continue to take on U.S. clients if he chose to do so.

But “as a practical matter, someone under indictment would not necessarily want to become subject to SEC regulations,” said Barry Barbash, a former director of the SEC’s investment- management division and now a partner at Willkie Farr & Gallagher LLP. “They can be audited, the SEC can look at their books and records. They can see what kind of activity he’s engaged in. There’s a whole host of things they can do.”

The SEC declined to comment.

Beck, 49, is one of about 30 Swiss advisers who have been indicted in the U.S. since 2008, part of a broad probe of tax evasion and undeclared offshore accounts. At least 21 are still at large, including Beck. More than 50,000 Americans have avoided prosecution by disclosing undeclared accounts, paying over $7 billion. Separately, offshore banks have agreed to pay more than $4 billion in U.S. fines, penalties and restitution.

Federal prosecutors haven’t sought the extradition of the indicted Swiss advisers because Switzerland generally won’t extradite its own citizens.Family Business

After a brief meeting in the lobby of his apartment building, Beck declined, via e-mail, to comment. Any discussion of the two firms “may affect me and my family’s private sphere, which I need to protect,” he wrote.

“People are indicted all the time,” said Dustin Milne, the Zurich attorney representing Beck’s company, Beck Verwaltungen AG, and his sons’ firm, which manages $22.7 million for a handful of mostly wealthy Americans in New York and Florida, according to an SEC filing. “Should the family stop being interested in running the family business? Should they stop looking for opportunities that they heard about at the dinner table?”

Milne, who spoke on behalf of the two companies, said Beck’s firm no longer has U.S. clients and that he “has no ownership, management or influence on investment advisory services of Beck Asset Management,” or BAM, the entity owned by his sons.‘Natural Process’

He said it was likely that clients from Beck’s firm would have joined his sons’ company as clients. That “would be a natural process and something that BAM would have anticipated at the outset, as both companies serve the same type of clientele, i.e., the Jewish investment community.”

Although SEC filings show that Beck’s sons are the owners of the new firm, Milne said neither man plays a role in the daily business of Beck Asset Management. Efrajim Beck is in the commercial real estate business and Naftali is chief financial officer for a different firm, according to the lawyer. He said the two men are in their late 20s.

For decades, Beck worked closely with UBS, meeting in the bank’s offices to set up accounts that weren’t declared to the U.S. Internal Revenue Service, prosecutors say. He specialized in helping Orthodox Jews in Brooklyn, according to two people familiar with the matter. UBS declined to comment.

In one case, a New York client who needed funds from an offshore account was directed by an anonymous caller to drive to a Brooklyn address. When the client pulled up, a 5-year-old child walked out of the house and handed over a brown paper bag, according to the indictment. Inside was approximately $150,000 in cash.New Bank

When news broke in 2008 that federal prosecutors were probing UBS, Beck allegedly helped clients move money to Wegelin & Co., then Switzerland’s oldest private bank, hoping to avoid U.S. detection, according to the indictment.

The space shared by his firm and his sons’ firm on the fourth floor of a Zurich office building is still one story above a UBS office. Wegelin closed in 2013 after pleading guilty in the U.S. to conspiracy to evade taxes.

Isak Mosbacher, who simultaneously serves as “relationship manager” for both Beck Asset Management and Beck Verwaltungen, declined to comment.

Beck’s company and that of his two sons are independent from one another, Milne wrote in an e-mail. And the two firms share space because it’s cost-efficient, he said.

“While the office space is a shared office, the advisory businesses are completely independent, i.e., independent investment committees, separate IT systems with firewall protections, separate archiving,” Milne said.

“Yes, they are his sons; yes, they share common office space,” he said. “But none of that concludes, therefore, Mr. Beck is doing his old U.S. business.”