A Swiss banker who claims to have handed WikiLeaks details of rich tax evaders went on trial on Wednes0day to answer charges of coercion and breaking Switzerland's strict banking secrecy laws.

Zurich prosecutors allege that Rudolf Elmer stole client data after being fired from his job at the Cayman Islands branch of Julius Baer, and then tried to extort money from the Swiss-based bank and its senior executives.

Prosecutor Alexandra Bergmann also alleges that Elmer, 55, illegally gave details on the bank's offshore clients to tax authorities, media and later WikiLeaks.

On Monday, Elmer staged a dramatic ceremony in London, where he handed over two more data CDs to WikiLeaks founder Julian Assange. Elmer claimed the disks contained names of 2,000 wealthy account holders, but refused to give details of the companies or individuals involved.

The case has generated intense interest abroad because of the link to WikiLeaks, and in Switzerland, where bank client privacy has a special place in the national psyche.

Several Swiss banks including UBS AG and Credit Suisse Group have suffered embarrassing data leaks in recent years, some at the hands of disgruntled employees.

Prosecutors are calling for an eight-month sentence and fine for what Julius Baer says was a vendetta by a disgruntled employee against it.

Elmer claims he was trying to expose a widespread system of tax evasion by rich businesspeople and politicians.

Elmer's actions caused a US judge to shut down WikiLeaks for two weeks in early 2008, marking the only time that the secrecy-spilling website has been forced offline for a significant amount of time.

Since then, WikiLeaks has shot into public consciousness for publishing thousands of secret US military and diplomatic files.

US authorities are currently trying to build a legal case against WikiLeaks and some of its collaborators, claiming the release of the files puts lives at risk.

Appearing before a single judge at Zurich's administrative court today, Elmer admitted sending threatening messages to some bank officials, but insisted he had done so after the bank fired him from his job at its Cayman Islands branch and then intimidated him.

"I was in an extreme situation," he said. "It's logical that I developed a defense strategy."

He denied issuing a bomb threat against the bank, but admitted threatening to send details of the bank's exclusive offshore clients to tax authorities in Switzerland, Britain and the United States.