The Swiss prosecutor said Friday it has taken one person into custody as part of an investigation into data allegedly stolen from Swiss bank Credit Suisse Group (CS) and later sold to German officials.

Zurich-based Credit Suisse declined to comment.

The arrest comes nearly one year after a major bank data theft involving German clients of Swiss banks became public and several months after a man suspected of stealing the data and selling it was found dead in his Swiss prison cell in an apparent suicide. The federal prosecutor, which doesn't mention Credit Suisse specifically in its statement, didn't elaborate on what the relationship between the person in custody and the deceased might have been.

"The current probe demands further investigational measures constantly. We cannot comment in detail at the moment."

The investigation comes as Switzerland faces intense international scrutiny over its banking-secrecy laws, which many governments believe encourage tax evasion.

In 2009, Switzerland partly succumbed to pressure and loosened secrecy laws, without giving them up altogether.

As part of the efforts by German authorities to crack down on alleged tax evaders, who are believed by German officials to hold around EUR175 billion in assets in Switzerland, offices of Credit Suisse Group had been searched in Germany last summer. Credit Suisse said last year that it believes it "has been the victim of a data theft." The bank since filed criminal charges against the individuals who committed the data theft.

Germany's dogged pursuit of several cases has led to tensions with Switzerland, which has said it won't cooperate with criminal investigations that are based on evidence that was stolen from Swiss banks. Since then, the two countries have agreed to begin talks to hammer out tax pacts, which include a withholding tax on investment income of Germans clients with Swiss accounts and transferring the tax receipts to the German authorities.

-By Katharina Bart, Dow Jones Newswires; +41 43 443 8043; katharina.bart@dowjones.com