The Justice Department ... made public detailed memos describing brutal interrogation techniques used by the Central Intelligence Agency, as President Obama sought to reassure the agency that the C.I.A. operatives involved would not be prosecuted. In dozens of pages of dispassionate legal prose, the methods approved by the Bush administration for extracting information from senior operatives of Al Qaeda are spelled out in careful detail - like keeping detainees awake for up to 11 straight days, placing them in a dark, cramped box or putting insects into the box to exploit their fears. The interrogation methods were authorized beginning in 2002, and some were used as late as 2005 in the C.I.A.'s secret overseas prisons. The United States prosecuted some Japanese interrogators at war crimes trials after World War II for waterboarding and other methods detailed in the memos. Together, the four memos give an extraordinarily detailed account of the C.I.A.'s methods and the Justice Department's long struggle, in the face of graphic descriptions of brutal tactics, to square them with international and domestic law. Passages describing forced nudity, the slamming of detainees into walls, prolonged sleep deprivation and the dousing of detainees with water as cold as 41 degrees alternate with elaborate legal arguments concerning the international Convention Against Torture. The revelations may give new momentum to proposals for a full-blown investigation into Bush administration counterterrorism programs and possible torture prosecutions.