The Justice Department’s ethics office recently recommended that prosecutors investigate the prisoner abuse cases, reversing the Bush administration and potentially exposing C.I.A. workers and contractors to prosecution for their brutal treatment of detainees, according to a person officially briefed on the matter.

Mr. Durham is already steeped in legal issues related to the intelligence agency. He is currently investigating whether anyone broke the law when C.I.A. officials in 2005 destroyed videotapes of interrogation of top terror suspects.

Mr. Durham will examine several cases which were referred to the Justice Department by the C.I.A.’s Inspector General and were subsequently investigated and dropped by the Justice Department under President Bush. The cases were detailed in a 2004 report by the C.I.A. inspector general that was released on Monday by the Justice Department. The report outline cases of abused allegedly committed by C.I.A. personnel and contract employees, mainly in Iraq and Afghanistan.

In the spring of 2003, long before Abu Ghraib or secret prisons became part of the American vocabulary, a pair of recently hired lawyers at the American Civil Liberties Union noticed a handful of news reports about allegations of abuse of prisoners in American custody. The lawyers, Jameel Jaffer and Amrit Singh, wondered: Was there a broader pattern of abuse, and could a Freedom of Information Act request uncover it? The case has produced revelation after revelation: battles between the Federal Bureau of Investigation and the military over the treatment of detainees at the Guantánamo Bay prison camp; autopsy reports on prisoners who died in custody in Afghanistan and Iraq; the Justice Department’s long-secret memorandums justifying harsh interrogation methods; and day-by-day descriptions of what happened inside the Central Intelligence Agency’s overseas prisons.

“This is certainly a landmark case in every respect, including in the history of the Freedom of Information Act,” said Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists and an expert on the act.

But Mr. Aftergood said the case also illustrated how costly litigation was often necessary to unearth documents the government preferred to protect. “The law gives you standing to fight,” he said. “It doesn’t guarantee victory.”

After five years of often bitter internal debate, the Justice Department concluded in a report released Friday that the lawyers who gave legal justification to the Bush administration’s brutal interrogation tactics for terrorism suspects used flawed legal reasoning but were not guilty of professional misconduct.