Washington ? President Barack Obama absolved CIA officers from prosecution for harsh, painful interrogation of terror suspects Thursday, even as his administration released Bush-era memos graphically detailing — and authorizing — such grim tactics as slamming detainees against walls, waterboarding them and keeping them naked and cold for long periods.

Human rights groups and many Obama officials have condemned such methods as torture. Bush officials have vigorously disagreed.

In releasing the documents, the most comprehensive accounting yet of interrogation methods that were among the Bush administrations most closely guarded secrets, Obama said he wanted to move beyond “a dark and painful chapter in our history.”

Past and present CIA officials had unsuccessfully pressed for more parts of the four legal memos to be kept secret, and some critics argued the release would make the United States less safe.

Michael Hayden, who led the CIA under George W. Bush, said CIA officers will now be more timid and allies will be more reluctant to share sensitive intelligence.

“If you want an intelligence service to work for you, they always work on the edge. That’s just where they work,” Hayden said. Now, he argued, foreign partners will be less likely to cooperate with the CIA because the release shows they “can’t keep anything secret.”

On the other side, human rights advocates argued that Obama should not have assured the CIA that officers who conducted interrogations would not be prosecuted if they used methods authorized by Bush lawyers in the memos.

Obama disagreed, saying in a statement, “Nothing will be gained by spending our time and energy laying blame for the past.”

The Bush administration memos describe the tough interrogation methods used against 28 terror suspects, the fullest and now complete government accounting of the techniques. They range from waterboarding — simulated drowning — to using a plastic neck collar to slam detainees into walls.

Other methods were more psychological than violent. One technique approved but never used involved putting a detainee who had shown a fear of insects into a box filled with caterpillars.

Even as they exposed new details of the interrogation program, Obama and Attorney General Eric Holder offered the first definitive assurance that the CIA officials who were involved are in the clear, as long as their actions were in line with the legal advice at the time.