WASHINGTON — Over 14 years in American custody, Abu Zubaydah has come to symbolize, perhaps more than any other prisoner, how fear of terrorism after the Sept. 11, 2001, attacks changed the United States.

He was the first detainee to be waterboarded, and his brutal torture was documented in a Senate report. He is among those held without charges and with no likelihood of a trial. The government long ago admitted that he was never the top leader of Al Qaeda it claimed he was at the time of his capture in 2002, but it insists that he may still be dangerous.

In all that time, Mr. Zubaydah, now 45, had never been seen by the outside world. That changed on Tuesday, as his calm face was beamed via video feed from the Guantánamo Bay military prison to a Pentagon conference room.

In a long-postponed hearing, he argued, through a statement read by a uniformed soldier, that he posed no threat and should be released. A profile prepared by the Defense Department, also read aloud, concluded with unsettling ambiguity that he “probably retains an extremist mind-set.”