The FBI is investigating 26 unsolved civil-rights era cases out of nearly 100 referred to the bureau over the last year, according to Director Robert Mueller.

Mueller, who was set to testify Wednesday at an FBI oversight hearing before the Senate, also described the protection of civil liberties as one of his top priorities. Lawmakers were expected to press him about whether his agents violated the civil rights of U.S. citizens whose personal information was obtained secretly in terror and spy investigations.