Some of the secrets of Switzerland's biggest bank were put on display on Tuesday as federal authorities indicted a former UBS banker on charges of helping a wealthy American real estate developer evade taxes.

The one-count conspiracy indictment, unsealed in federal court, accuses the former banker, Bradley Birkenfeld, of helping the developer evade taxes on $200 million held in bank accounts in Switzerland and Liechtenstein. The indictment also names as a co-conspirator Mario Staggl, an executive at a trust company in Liechtenstein, a major European tax haven.

An official briefed on the investigation identified the developer as Igor Olenicoff, the billionaire founder of Olen Properties. A lawyer for Mr. Olenicoff, Edward M. Robbins Jr., declined to comment, as did Mr. Olenicoff when contacted by e-mail.

The indictment is part of a widening federal investigation into whether UBS, one of the world's largest money managers for the wealthy, helped certain clients evade taxes, and it suggests that American authorities are stepping up scrutiny of offshore tax transactions. The inquiry focuses on UBS's private bank based in Zurich, which does much of its business through Liechtenstein.

Martin Liechti, a top private banker at UBS, recently was detained briefly by federal authorities in Florida as a material witness in the investigation.

Mr. Birkenfeld, 43, a citizen of the United States, was the director of important clients for UBS in Geneva from 2002 to 2006, and is a partner and chairman at Union Charter, which caters to wealthy investors through offices in Geneva, Dubai and Hong Kong. Mr. Staggl, also 43, is a co-founder of the New Haven Trust Company in Liechtenstein, which specializes in tax planning.

Mr. Birkenfeld made an initial appearance on Tuesday in the United States District Court for the Southern District of Florida in Fort Lauderdale. Mr. Staggl, who is a citizen of Liechtenstein, remains at large and did not respond to e-mail messages.

According to the indictment, the two men created fictitious trusts and bogus corporations to conceal the ownership and control of offshore assets. They also advised clients to destroy bank records and helped them file false tax returns, the indictment said.

The two men and others made several trips to the United States to pitch tax plans that were intended to conceal American bank clients' ownership of accounts in a Swiss bank, the indictment said.

The plans enabled UBS to avoid its obligations to disclose certain income information to the I.R.S., the indictment said, while also evading certain American tax requirements. The cornerstone to the defendants' pitch was that Swiss and Liechtenstein bank secrecy was impenetrable, the indictment said.

UBS declined to comment on the charges.

In December, Mr. Olenicoff pleaded guilty to tax evasion and to lying on his tax returns, and agreed to pay back taxes totaling $52 million. Mr. Olenicoff, who was born in Russia and emigrated to the United States decades ago, is on the Forbes 400 list of wealthiest people, with an estimated net worth of $1.7 billion.

The developments come at a difficult time for UBS, which has been hit by hard by the credit crisis. The bank has suffered write-downs of about $38 billion since last summer, leading to the departure of a chief executive, a chairman and other senior managers.