Moments after planes crashed into the World Trade Center and the Pentagon, lawyers in the Justice Department's elite Office of Legal Counsel began crowding into the office of one of the agency's newest deputies, John C. Yoo, to watch the horror unfold on his television set.
"We all stood around watching this event, and he just seemed very calm, like he wasn't going to let these terrorists stop him from doing his work," recalled Robert J. Delahunty, a friend of Mr. Yoo's who worked in the office.
Fearful of another attack and told that all "nonessential personnel" should evacuate, Mr. Delahunty and others streamed out of the department's headquarters and walked home. Mr. Yoo, then a 34-year-old former law professor whose academic work had focused on foreign affairs and war-powers issues, was asked to stay behind, and he quickly found himself in the department's command center, on the phone to lawyers at the White House.
Within weeks, Mr. Yoo had begun to establish himself as a critical player in the Bush administration's legal response to the terrorist threat, and an influential advocate for the expansive claims of presidential authority that have been a hallmark of that response.
While a mere deputy assistant attorney general in the legal counsel office, Mr. Yoo was a primary author of a series of legal opinions on the fight against terrorism, including one that said the Geneva Conventions did not apply and at least two others that countenanced the use of highly coercive interrogation techniques on terror suspects. Recently, current and former officials said he also wrote a still-secret 2002 memorandum that gave legal backing to the administration's secret program to eavesdrop on the international communications of Americans and others inside the United States without federal warrants.