WASHINGTON â In the aftermath of the Sept. 11 attacks, CIA operatives were allowed to shackle, strip and waterboard terror suspects. Now, President Barack Obama has assured these operatives that they will not be prosecuted for their rough interrogation tactics. At the same time, Obama's attorney general offered the operatives legal help if anyone else takes them to court over the harsh interrogation methods that were approved by the Bush administration. The offer of presidential support, however, did not extend to those outside the CIA who approved the so-called enhanced interrogation methods or any CIA officers who may have gone beyond what was allowed in four legal memos written in 2002 and 2005 that the Obama administration released Thursday. The Bush administration memos authorized keeping detainees naked, in painful standing positions and in cold cells for long periods of time. Other techniques included depriving them of solid food and slapping them. Sleep deprivation, prolonged shackling and threats to a detainee's family also were used. In releasing the documents, the most comprehensive accounting yet of interrogation methods that were among the Bush administration's most closely guarded secrets, Obama said he wanted to move beyond "a dark and painful chapter in our history." Parts of the four memos were blacked out, and past and present CIA officials had pressed unsuccessfully for larger portions of the documents to be kept secret. Some critics argued that the release of the memos would make the United States less safe. Michael Hayden, who led the CIA under President George W. Bush, said CIA officers now will 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 government accounting of the techniques to date. They range from waterboarding â or simulated drowning â 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. The documents also offer justification for using the tough tactics. A memo dated May 30, 2005, says that before the harsher methods were used on top al-Qaida detainee Khalid Sheikh Mohammed, he refused to answer questions about pending plots against the United States. "Soon, you will know," he told them, according to the memo. It says the interrogations later extracted details of a plot called the "second wave" to use East Asian operatives to crash a hijacked airliner into a building in Los Angeles. Terror plots that were disrupted, the memos say, include the alleged effort by Jose Padilla to detonate a "dirty bomb" spreading radioactive materials by means of conventional explosives. 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 complied with the legal advice at the time. Holder went further, telling the CIA that the government would provide free legal representation to its employees in any legal proceeding or congressional investigation related to the program, and would repay any financial judgment. "It would be unfair to prosecute dedicated men and women working to protect America for conduct that was sanctioned in advance by the Justice Department," Holder said. Obama said in his statement and a separate letter sent directly to CIA employees that the nation must protect their identity "as vigilantly as they protect our security." Current CIA Director Leon Panetta said in a message to his employees: "CIA responded, as duty requires." Panetta had been among those seeking to have more of the memos blacked out, according to a government official who declined to be identified because he was not authorized to release the information. The CIA has acknowledged using waterboarding on three high-level terror detainees in 2002 and 2003, with the authorization of the White House and the Justice Department. Hayden said waterboarding has not been used since, but some human rights groups have urged Obama to hold CIA employees accountable for what they, and many Obama officials, say was torture. The memos produced by the Justice Department's Office of Legal Counsel were released to meet a court-approved deadline in a lawsuit against the government in New York by the American Civil Liberties Union. "It's impossible not to be shocked by the contents of these memos," ACLU lawyer Jameel Jaffer said. "The memos should never have been written, but we're pleased the new administration has made them public."