CIA interrogators who used waterboarding on terrorism suspects will not face prosecution, President Barack Obama said in releasing Bush-era memos specifying that the practice did not constitute torture. Obama affirmed his administration's unwillingness to prosecute under antitorture laws CIA personnel who relied in good faith on Bush administration legal opinions issued after the September 11 attacks. The four memos Obama released approved techniques including waterboarding, week-long sleep deprivation, nudity and putting insects in with a tightly confined prisoner. Obama was trying to balance between showing the world he would break with former President George W. Bush over the widely condemned treatment of terrorism suspects, and preserving the effectiveness of his intelligence agencies. The Obama administration also said it would try to shield CIA employees from any international or foreign tribunal -- an immediate challenge to Spain, where a judge has threatened to investigate Bush administration officials.