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.