It was some hours after the World Trade Center towers had been toppled when Sulaiman Abu Ghaith was summoned to a meeting with Osama bin Laden. He recalled a three-hour-or-so drive into the night, finding the leader of Al Qaeda in a cave amid the mountains in Afghanistan.

Bin Laden wanted his opinion on what would happen next, Mr. Abu Ghaith testified on Wednesday. He said he told Bin Laden that he was not a military analyst, but Bin Laden pressed him.

Mr. Abu Ghaith said he told him that “America, if it was proven that you were the one who did this, will not settle until it accomplishes two things: to kill you and topple the state of Taliban.

“He said, ‘You are being too pessimistic.’

“I said, ‘You asked my opinion, and this is my opinion.’ ”