Societe Generale spokeswoman Laura Schalk confirmed that investigators searched its offices on Wednesday, taking some records and detaining the employee, whose name she declined to provide. She called the search part of "normal proceedings" in the probe.

Christophe Reille, a spokesman for Kerviel, declined to comment.

A French court is scheduled to rule Friday on whether Kerviel should be freed from a Paris prison during the investigation. Investigators have said they want to prevent him from speaking with any possible accomplices.

Kerviel says he acted alone, but that his bosses must have been aware of his massive risk-taking, and turned a blind eye as long as he was making money for the bank. Investigators are searching for others who could have known about, or participated in, what the bank says was Kerviel's unauthorized activity.

A preliminary internal probe by Societe Generale found no evidence that anyone helped Kerviel hide his positions. The report did say bank officials failed to follow up on 74 warnings about questionable trades, uncovering Kerviel's positions only on the 75th.

Kerviel's lawyer Guillaume Selnet told The Associated Press last week he will be asking why the alerts "didn't provoke any reaction."

Societe Generale says Kerviel forged documents and e-mails to suggest he had hedged his positions.

The bank reported a trading loss of nearly 4.9 billion euros ($7.58 billion) on Jan. 24 from liquidating 50 billion euros ($73 billion) in unauthorized futures positions Kerviel had taken.