A former UBS AG banker was charged in Florida with helping a billionaire real-estate developer evade American taxes on $200 million in Swiss and Liechtenstein bank accounts.

The one-count conspiracy indictment, unsealed in Fort Lauderdale, accuses a “director of key clients” for UBS from 2002 to 2006, Bradley Birkenfeld, and Mario Staggl of Liechtenstein of falsifying documents, failing to prepare tax forms, and using other tactics to help the billionaire evade American taxes.

Mr. Birkenfeld, 43, made an initial appearance in court today; Mr. Staggl, 43, remains at large, the Justice Department said.

The indictment was the latest action in an American investigation into whether UBS helped clients evade taxes. UBS’s head of international wealth management for the Americas, Martin Liechti, was detained by American authorities as a “material witness” in the investigation, the Financial Times reported earlier this month.

The investigation added to trouble swirling around the biggest Swiss bank, which has also been hit hard by the subprime loan crisis.Clients pulled a net $12.1 billion from UBS’s asset- and wealth-management units in the first quarter, the first withdrawal in almost eight years as the bank’s writedowns swelled to $38 billion. UBS said last week that the Justice Department is investigating its conduct involving tax issues between 2000 and 2007.

“The bank is continuing to cooperate with this investigation,” a UBS spokeswoman in New York, Rohini Pragasam, said yesterday. “It is not appropriate to comment on charges brought against a former UBS employee.”

Messrs. Birkenfeld and Staggl didn’t immediately return e-mails seeking comment.

The indictment alleges Messrs. Birkenfeld and Staggl attempted to sidestep rules in an American-Swiss tax treaty that require information to be exchanged on some financial transactions. The pair — and others not identified by prosecutors — allegedly traveled to America to pitch their schemes.