The trial of an ex-banker accused of breaching Swiss banking secrecy laws by handing over confidential data about offshore clients to WikiLeaks was stopped on Wednesday after the defendant collapsed.

Rudolf Elmer, a former senior executive at Julius Baer, fainted outside the courtroom in Zurich after earlier complaining of a headache. The 59-year-old, who denies the charges, was taken to hospital by ambulance.

A spokesman for the court said it was unclear when the trial would resume.

The former banker has been under investigation since 2011 for giving WikiLeaks founder Julian Assange two compact discs during a news conference in London. Elmer said at the time they contained confidential data on about 2,000 offshore banking clients, but on Wednesday he told the court they were empty.

Elmer, who has previously described himself as a “Gandhi of Swiss tax law” and said he wants to draw attention to financial abuses, was charged in July. He could face up to four-and-a-half years in jail if found guilty of illegally handing over client data.

He is also accused of attempting to pass confidential client files to the German finance ministry in 2009, a charge he denies.

Before his collapse, the former banker had denied breaking banking secrecy, replying yes to the judge’s question of whether he felt innocent.

The case also comes amid moves by Switzerland to preserve domestic banking secrecy after, under international pressure, it agreed in May to join other countries in sharing tax information for international account holders.

Elmer is the latest high-profile financial whistleblower case in Switzerland, following that of the former Credit Suisse and UBS employee Bradley Birkenfeld and the ex-HSBC Switzerland banker Herve Falciani.

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