Previously undisclosed Justice Department e-mail messages, interviews and newly declassified documents show that some of the lawyers, including James B. Comey, the deputy attorney general who argued repeatedly that the United States would regret using harsh methods, went along with a 2005 legal opinion asserting that the techniques used by the Central Intelligence Agency were lawful.

That opinion, giving the green light for all 13 C.I.A. methods, including waterboarding and up to 180 hours of sleep deprivation, “was ready to go out and I concurred,” Mr. Comey wrote to a colleague in an April 27, 2005, e-mail message obtained by The New York Times.

While signing off on the techniques, Mr. Comey in his e-mail provided a firsthand account of how he tried unsuccessfully to discourage use of the practices.