"Athan Theoharis, a pre-eminent historian of the F.B.I. whose indefatigable research into the agency's formerly unobtainable files produced revelations about decades of civil liberties abuses under the leadership of J. Edgar Hoover, died on July 3.

"Beginning in the mid-1970s, Professor Theoharis, who taught history at Marquette University in Milwaukee, deftly used Freedom of Information Act requests to pry open the F.B.I.'s deep well of secrets, including the extent to which Hoover compiled damning information on public officials and his cooperation with Senator Joseph McCarthy's campaign against people he accused of being Communists.

"'Hoover was an insubordinate bureaucrat in charge of a lawless organization,' Mr. Theoharis told The Milwaukee Journal Sentinel in 1993. 'He was also a genius who could set up a system of illegal activities and a way to keep all documentation secret for many years.'

"Professor Theoharis's strategic use of the Freedom of Information Act, or FOIA, enabled him to find pathways to documents through a purposely evasive filing system that Hoover had hoped no one would ever divine."

Another hero of open government passes into history, but his legacy survives to inspire others.