Police questioned former banker Rudolf Elmer on Thursday over possible fresh breaches of Swiss bank law for giving data to WikiLeaks this week, a day after he was found guilty of violating bank secrecy.
Authorities have 48 hours from Elmer's arrest to decide whether they have grounds to hold him in custody for longer, state prosecutor Peter Pellegrini said on Thursday.
The prosecutor's office confirmed that Elmer had been questioned, but declined to provide further details.
Elmer was taken into custody by police on Wednesday evening, hours after he was convicted of breaching strict banking secrecy by passing on private client data and of threatening employees at his former firm Julius Baer.
Jack Blum, a former US Congressional investigator and Washington lawyer who has been advising Rudolf Elmer, told Reuters he was puzzled and dismayed by the Swiss authorities move to re-arrest Elmer.
He appeared with Elmer at a London news conference earlier this week when the former Swiss banker handed over to WikiLeaks founder Julian Assange computer discs which Elmer indicated contained details of as many as 2,000 offshore bank accounts.
A source familiar with the data said it contained information about offshore banking "structures" but might not include information which would constitute obvious proof of wrongdoing by specific individuals.
Blum questioned whether Swiss authorities had any solid basis for believing the discs' contents included data from Switzerland.
"The Swiss are just angry because of the attention (Elmer's latest actions) have put on their system of secrecy. I think that attention is well deserved," Blum 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 neighbouring Germany buying secret data from informants to track down tax evaders.
A decision on whether to continue detaining Elmer, who helped bring WikiLeaks to prominence three years ago when he used it to publish secret client details, would depend on whether the state had a case against him and whether there was a risk of him taking flight, Pellegrini said.
Elmer was held for a month in 2005 when he was arrested on the charges that led to Wednesday's prosecution -- which did not concern WikiLeaks. His wife and daughter live near Zurich.
A source who spoke to Elmer's wife Heidi after his arrest said she reported that police arrived at their residence in a village outside Zurich with a search warrant and a warrant for Elmer's arrest.
Lucius Blattner, whose firm represented Elmer in Wednesday's proceedings, said his firm would again represent the former banker in the case of further legal action.
On Wednesday, the court sentenced Elmer to a fine of 7,200 Swiss francs ($7,505), suspended for two years, without giving reasons, which will be presented in a written judgement. The defence will decide whether to appeal within 10 days.