An American court watched five minutes of footage of people jumping out of the World Trade Center today as jurors were asked to give the death sentence to Zacarias Moussaoui, the so-called "20th hijacker", and the only man charged in the America in connection with the September 11 attacks.

Many in the court gasped and wept as they watched the images, which were followed by testimony from Rudolph Giuliani, a former mayor of New York, who said that he thought every day of those who leapt to their deaths on 9/11.

The jarring evidence was put forward by prosecutors for the climax of the "death penalty phase" of the trial of Moussaoui, in which the personal toll of a crime must be demonstrated.

This stage of proceedings is considered a relative formality after prosecutors cleared the more difficult hurdle of proving that Moussaoui, an admitted member of al-Qaeda, could have prevented the attacks after he was arrested in Minnesota in August 2001.

On Monday, jurors at the heavily-guarded court in the suburbs of Alexandria, Virginia, decided that Moussaoui was directly responsible for at least one death on September 11 after he told the court that he knew the details of the plot and had trained to hijack an aircraft himself.

Moussaoui's extraordinary confession, which also implicated Richard Reid, the British "shoe-bomber" convicted for trying to blow up an airliner in October 2001, contradicted his earlier statements and evidence from other members of al-Qaeda. His lawyers say he is schizophrenic and trying to become a martyr for extremist Islam.

Today Mr Giuliani, who is revered for his leadership in New York on the day and after the attacks, told the court what he saw and remembered from September 11.

"I saw several people, I can’t remember how many, jumping," he said. "There were two people right near each other. It appeared to me they were holding hands. Of the many memories, that’s one that comes to me every day."

Sitting next to a scale model of the World Trade Center, Mr Giuliani said it was clear the city was under attack the moment the second aircraft struck the towers. When the buildings collapsed, he said: "It was horrid. The worst thing I’ve ever seen in my whole life ... parts of human bodies ... hands or legs."

Today's evidence will be followed by a series of videos, tape recordings and pieces of written testimony intended to prove the enormous trauma caused by the worst terrorist attack on American soil.

In the coming days, the US Department of Justice has already said that it intends to introduce 45 "impact statements" from the relatives of those who died. The names and photographs of all 2,972 victims of the atrocity will be put before the jury.

Last night US District Judge Leonie Brinkema also decided to allow cockpit recordings from United Airlines flight 93, which crashed into a field in Pennsylvania after passengers fought back against their hijackers, to be played in court. The last moments of the flight have never made available to the public and Judge Brinkema has told the relatives of those killed that they have until Tuesday to decide whether the jury hears the tapes in private.

The story of flight 93 is also the subject of a Hollywood film, made with the co-operation of some of the families, which is due to be released later this month and in the UK in September. Trailers of the film, which will premiere at the Tribeca Film Festival in New York, have already prompted some cinema audiences in Manhattan to walk out in distress.

In the last days of the trial, Moussaoui's increasingly exasperated lawyers, Edward MacMahon and Gerald Zerkin, are expected to argue that their client, who was born in Morocco and grew up in France, suffered a childhood of racism, alienation and mental illness. They will also warn the jury that Moussaoui is desperate to become a martyr for a movement that never quite accepted him.

Today Mr Zerkin called his client a "wannabe al-Qaeda suicide pilot who could not fly and did not have a crew".

"The government’s evidence will present an extraordinary challenge for you," said Mr Zerkin. "You must somehow maintain equilibrium. You must nevertheless open yourselves to the possibility of a sentence other than death."

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