ALEXANDRIA, Va. – Prosecutors yesterday summoned the voices of the dead from the September 11 attacks to convince jurors that the would-be suicide pilot Zacarias Moussaoui should be put to death.

Opening the final phase of the proceedings against the Moroccan-born terrorist, prosecutor Rob Spencer read from the transcript of an emergency call made by a female victim trapped on the 83rd floor of the World Trade Center as she was “engulfed” in smoke and flames.

“We’re on the floor and we can’t breathe … I don’t see any more air … I’m going to die, aren’t I?”

On a day of drama at a federal court in Alexandria, Va., the state also summoned a surprise witness, the former New York mayor Rudy Giuliani, who testified for the first time about the attacks.

Mr. Spencer, preparing the jury for the experience of hearing the recordings of so many victims’ last moments, said there was no other way to convey the enormity of September 11, 2001, and Moussaoui’s role in it.

“You cannot understand the magnitude of that day unless you hear it from the victims themselves,” he said.

Moussaoui, 37, a former worshipper at a mosque in Brixton, south London, trained with Al Qaeda in Afghanistan and is the only person to have been tried in America in connection with the September 11 attacks.

He has already been judged eligible for execution. The jury must now decide whether he acted in a heinous and depraved manner, the legal tests for those to be killed by the state.

Although Moussaoui was arrested while attending a flight training school in Minnesota a month before the atrocities, he admitted lying to protect the conspirators and said he had hoped to become a suicide pilot in a separate mission.

Thursday he smiled and laughed as, a few feet away, victims’ families sat weeping and covering their eyes to blank out photographs being displayed in court.

Mr. Giuliani said that until he reached the twin towers, he had discounted early reports that people were jumping out of the building. Then he saw a couple falling, hand-in-hand.

“I froze. I realized in that couple of seconds, it switched my thinking and emotions. I said, ‘We’re in uncharted territory.'”

The defense acknowledged that much of the testimony would be highly emotive. But Gerald Zerkin, one of Moussaoui’s court-appointed lawyers, asked jurors not to be swayed and to consider “the possibility of a sentence other than death”.

He said Moussaoui had fallen under the spell of radical Muslims in London and described Moussaoui as a “wannabe Al Qaeda suicide pilot who could not fly and did not have a crew”.

The defense will also call expert witnesses to testify that the erratic Moussaoui may be schizophrenic.