A Swiss court yesterday said it lacked clear evidence to rule on an appeal by a former Swiss banker turned WikiLeaks whistleblower against his conviction for breaching Switzerland’s strict banking secrecy after he revealed private client data.

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

Judge Peter Marti said on Thursday 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.

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.

Swiss bank secrecy has come under global attack in recent years, as cash-strapped governments seek to boost revenue by cracking down on tax cheats.

Switzerland last year gave details of about 4,450 UBS accounts to U.S. authorities as part of a deal to settle a tax probe into its biggest bank despite strict secrecy laws.