The report said never before had there been "the kind of considered and detailed discussions that occurred after 9/11 directly involving a president and his top advisers on the wisdom, propriety and legality of inflicting pain and torment on some detainees in our custody."
Debate over harsh interrogation methods used during President George W. Bush's administration has fallen along largely partisan lines, but the Constitution Project's task force on detainee treatment was led by two congressional members with White House experience, Republican Asa Hutchinson and Democrat James R. Jones, The New York Times reported.
The 11-member task force did not have access to classified records but it is the most ambitious independent attempt so far to assess the detention and interrogation programs, the Times said.
The report, to be posted on the project's website Tuesday, calls for the revision of the Army Field Manual on interrogation to eliminate Appendix M, which the panel said would permit an interrogation for 40 consecutive hours, and restore an explicit ban on stress positions and sleep manipulation, the Times said.
In the appendix is a 22-page legal and historical analysis explaining why the task force concluded that what the United States did constituted torture, the Times said. The appendix entry provided dozens of legal cases in which similar treatment was prosecuted in the United States or denounced as torture by American officials when used by other countries.
A report by the Senate Intelligence Committee based solely on CIA records and not interviews remains classified.
"As long as the debate continues, so too does the possibility that the United States could again engage in torture," said the report by the Constitution Project, a legal research and advocacy group.
The use of torture, the report concludes, has "no justification" and "damaged the standing of our nation, reduced our capacity to convey moral censure when necessary and potentially increased the danger to U.S. military personnel taken captive."
The Constitution Project study was begun after President Obama decided in 2009 not to support a national commission to investigate post-9/11 counter-terrorism programs, the Times said. The panel studied the treatment of prisoners at the Guantanamo Bay, Cuba, military prison, in Afghanistan and Iraq, and in the CIA's network of secret prisons. Staff members went to detention sites and interviewed dozens of former U.S. and foreign officials, as well as ex-detainees.
The task force said it couldn't find evidence that such interrogation methods produced valuable information that could not have been obtained by other means, the Times said.
Among other things, it confirms a report by Human Rights Watch that at least one Libyan militant was waterboarded by the CIA, contradicting the agency's saying only three al-Qaida prisoners were subjected the simulated drowning technique.
"This has not been an easy inquiry for me, because I know many of the players," Hutchinson, who was the head of the Drug Enforcement Administration and a Department of Homeland Security undersecretary during the Bush administration, told the Times. "But I just think we learn from history. ... It's incredibly important to have an accurate account not just of what happened but of how decisions were made.
He said he thought everyone involved in decisions acted in good faith.
Jones, a former ambassador to Mexico, said he didn't recognize "the depths of torture in some cases."
"We lost our compass," he said.