NEW YORK — Osama bin Laden’s hours in a dark Afghanistan cave the evening of the Sept. 11 attacks were brought to light when his son-in-law testified in his own defense at his terrorism trial, portraying the al-Qaida leader as worried and apprehensive as he contemplated how America would respond.

The son-in-law, Sulaiman Abu Ghaith, said the al-Qaida leader asked him hours after the attacks what he thought would happen next.

“Politically, I said, 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 the Taliban,” Abu Ghaith said he told him.

Bin Laden responded: “You’re being too pessimistic,” Abu Ghaith recalled in a discussion that he said went late into the night.

He said bin Laden had sent a messenger to pick him up earlier on Sept. 11 from a house in Kabul, Afghanistan, where he had watched the news unfold on television. He said bin Laden told him: “We are the ones who did it.”

He said he had met bin Laden only six or seven times previously before he was brought to the cave in a rough mountainous area.

The surprise testimony Wednesday by Abu Ghaith seemed to soften the image of the one-time Kuwaiti teacher and preacher known for fiery anti-American rhetoric on widely circulated post-attack videos until a prosecutor took his turn, eliciting damaging admissions from the 48-year-old defendant before showing a videotape on which Abu Ghaith spoke and included a hijacked plane slamming into a World Trade Center tower.

Questioned by defense lawyer Stanley Cohen and later by Assistant U.S. Attorney Michael Ferrara, the bearded Abu Ghaith testified that bin Laden seemed worried that night.