The Swiss prosecutor's office said on Friday former banker Rudolf Elmer would be detained over the weekend after police questioned him this week over possible fresh breaches of Swiss bank law.
Elmer was taken into custody by police on Wednesday after he handed over computer discs to WikiLeaks earlier this week. Elmer indicated the CDs contained details of as many as 2,000 offshore bank accounts.
In a separate case, Elmer was convicted on Wednesday of breaching banking secrecy by passing on private client data to the tax authorities and of threatening employees at his former firm Julius Baer. Elmer has appealed this verdict.
A judge will announce on Monday whether Elmer will be held for longer on remand, the prosecutor's office statement said.
Switzerland's bank secrecy helped it build a $2-trillion wealth management industry but the laws have come under intense global attack in recent years, with neighboring Germany buying secret data from informants to track down tax evaders.
(Reporting by Zurich Newsroom; Editing by Janet Lawrence)