Waterboarding involves strapping a suspect down and pouring water over his cloth-covered face to create the sensation of drowning. It has been traced back hundreds of years, to the Spanish Inquisition, and is condemned by nations around the world.
"We used it against these three detainees because of the circumstances at the time," Hayden told the Senate Intelligence Committee. "There was the belief that additional catastrophic attacks against the homeland were inevitable. And we had limited knowledge about al-Qaida and its workings. Those two realities have changed."
Hayden said Khalid Sheik Mohammed, Abu Zubayda and Abd al-Rahim al-Nashiri were waterboarded in 2002 and 2003. Hayden banned the technique in 2006, but National Intelligence Director Mike McConnell told senators during the same hearing Tuesday that waterboarding remains in the CIA arsenal - so long as it as the specific consent of the president and legal approval of the attorney general.
That prompted Sen. Dick Durbin, the Senate's No. 2 Democrat and a member of the Judiciary Committee, to call on the Justice Department to open a criminal inquiry into whether past use of waterboarding violated any law. The Pentagon has banned its employees from using waterboarding to extract information from detainees, and FBI Director Robert Mueller said his investigators do not use coercive tactics in interviewing terror suspects.
Durbin, already frustrated with Attorney General Michael Mukasey's refusal last week to define waterboarding a form of torture as critics have, said he would block the nomination of the Justice Department's No. 2 official if the criminal inquiry isn't opened.
It was a particularly sharp threat by Durbin, who represents Illinois - the same state that U.S. District Judge Mark Filip of Chicago, the deputy attorney general nominee, calls home.
"In light of the Justice Department's continued non-responsiveness to Congress on the issue of torture, including your disappointing testimony on waterboarding last week, I have reluctantly concluded that placing a hold on Judge Filip's nomination is my only recourse for eliciting timely and complete responses to important questions on torture," Durbin wrote in a letter to Mukasey on Tuesday.
He added: "A Justice Department investigation should explore whether waterboarding was authorized and whether those who authorized it violated the law."
Justice Department spokesman Brian Roehrkasse declined to comment except to say that the department "is reviewing the letter carefully."
The delay in confirming Filip could leave the Justice Department in leadership limbo following a year of internal upheaval and scandal, Mukasey, sworn in as attorney general in November, has made rebuilding the department a top priority for the final 11 months of the Bush administration.
Human Rights Watch, which has been calling on the government to outlaw waterboarding as a form of illegal torture, called Hayden's testimony "an explicit admission of criminal activity."
Joanne Mariner, the group's counterterrorism director, said Hayden's tesitimony "gives the lie" to the administration's claims that the CIA has not used torture. "Waterboarding is torture, and torture is a crime," she said.
Critics say waterboarding has been outlawed under the U.N.'s Convention Against Torture, which prohibits treatment resulting in long-term physical or mental damage. They also say it should be recognized as banned under the U.S. 2006 Military Commissions Act, which prohibits treatment of terror suspects that is described as "cruel, inhuman and degrading." The act, however, does not explicitly prohibit waterboarding by name.
During his own Senate appearance last week, Mukasey refused to declare waterboarding illegal, prompting Democrats to accuse him of potentially allowing the harsh interrogation tactic to be used in the future.
The attorney general said then he has reviewed Justice Department memos about the CIA's interrogation program and concluded that the spy agency doesn't currently engage in waterboarding. Beyond that, Mukasey would not discuss the legality of the classified program for fear of what he described as tipping off U.S. enemies about interrogation methods.
The Justice Department has long resisted exposing the Bush administration and its employees to criminal or civil charges or even international war crimes waterboarding is declared illegal. Hayden said interrogations have been conducted by both intelligence agents and government contractors interrogators but denied that the practice, as he described it, has been outsourced.
"This is a governmental activity under governmental direction and control in which the participant may be both government employees and contractors," he said in an exchange with Democratic Sen. Dianne Feinstein of California.
McConnell, the nation's spy chief, said in Tuesday's testimony that waterboarding "taken to its extreme, could be death; you could drown someone." But he, too, refused to declare it illegal in hypothetical cases.
"Everything I know is it is a legal technique used in a specific set of circumstances," McConnell said. "You have to know the circumstances to make a legal judgment," McConnell said.