Rudolf Elmer, who worked at the Cayman Islands branch of the Swiss private bank until he was fired in 2002, helped bring WikiLeaks to prominence when he used the site to publish bank documents to expose alleged tax evasion.

The news service reported that Judge Peter Marti said it was not clear whether the CD-roms Elmer had handed over contained data of bank clients in Switzerland or just in the Cayman Islands.

"If the data also originate from Zurich, the Swiss banking law also applies. We don't know precisely, however, what was on the CDs," Marti told the court, the report said.

He ordered the public prosecution service and Julius Baer to prove the origins of the data on the disk, placing the onus on the Swiss bank to publish client data.

Elmer’s actions have been a part of a series of assaults on Swiss bank secrecy. In at least one recent case, authorities in Germany paid for data stolen from a private bank, raising questions about states’ willingness to brush aside due process of law in their hunt for tax revenues.