'20th hijacker' says he plotted to fly a plane into the White House

Zacarias Moussaoui has testified that he and convicted "shoe bomber" Richard Reid were scheduled to fly a fifth hijacked plane into the White House as part of the terrorist plot of 11 September 2001 - and that he had lied to investigators after being arrested to enable the other attacks to go ahead.

Taking the stand in his own defence at his death penalty trial in Alexandria, Virginia, the self-confessed al-Qa'ida member said he knew that the World Trade Centre in New York was to be attacked but that he was unaware of the precise details of the conspiracy. "I had knowledge that the Twin Towers would be hit," he told the court.

Although he did not know the exact date, "I knew it would happen after August," said Moussaoui, who was taken into custody on 16 August 2001 in Minnesota, almost four weeks before the attacks on New York and Washington. The stunning, albeit partial, admissions have turned the case on its head. Together they make it much more likely that the only person thus far convicted of charges relating to 9/11 will now be sentenced to death, rather than spending the rest of his life behind bars.

Until the last, defence lawyers had fought to prevent their client giving evidence, fearing that he could do his case more harm than good. And yesterday he seemed to do precisely that.

Asked by prosecutors if he had lied to enable the attacks to go ahead, he replied: "Yes, you could say that." The admission is crucial. In order to secure the death penalty prosecutors have to show that if Moussaoui had immediately told investigators all he knew, at least some of the 3,000 deaths on that day could have been prevented.

But at least until Moussaoui took the stand, the focus had been on the blunder by a prosecution attorney who had illicitly coached key government witnesses, and on testimony that again highlighted the incompetence of the FBI in following up the leads it did have.

In the past, Moussaoui has been incoherent, abusive and, on occasion, hysterical. But this time, dressed in a green prison suit and white cap, he was calm and measured - even as his testimony directly contradicted what he had said before. Once again, he denied he was the missing "20th hijacker." But in an astonishing shift, he claimed that he was to taken part in a fifth hijacking that would have flown a plane into the White House, as part of the conspiracy. Previously Moussaoui had spoken of an attack on the White House, but only in a second wave of hijackings on an unspecified future date.

At first, Moussaoui told the court, he turned down a suggestion from the al-Qa'ida high command to become a suicide pilot. But he changed his mind in 2000, a year later, after having a dream which he discussed with Osama bin Laden. "My knowledge of the operation was very gradual. I didn't know from the start," he said. "I wasn't part of the operation at the beginning because I declined to be part of the operation." He admitted knowing by sight most of the 19 hijackers. But by the time of his arrest on immigration charges, Moussaoui said he was practicing for the mooted attack on the White House.

Reid was overpowered as he attempted to blow up a trans-atlantic passenger jet in December 2001. He was sentenced to life in prison in January 2003.