As part of the investigation, U.S authorities briefly detained a senior UBS-employee under a “material witness” warrant, but the staffer has not been charged with any wrongdoing, according to officials for Zurich, Switzerland-based UBS, Switzerland’s largest bank.

The Department of Justice and the Securities and Exchange Commission are examining whether UBS’ U.S clients sought to evade their U.S tax obligations with the assistance of advisers for the bank from 2000 to 2007, company officials said in a statement.

The senior staffer questioned was Martin Liechti, who heads UBS’ international wealth management business for the Americas, according to published reports. UBS officials would not confirm the identity of the employee.