The jury in the US trial of confessed al-Qaeda plotter Zacarias Moussaoui has decided he is eligible to face the death penalty when he is sentenced.
Moussaoui shouted a curse after the jury's verdict was read
A second phase of hearings will now take place, beginning on Thursday, to determine if he should be executed.
As the jury's verdict was announced in court, Moussaoui shouted: "You'll never get my blood, God curse you all."
Prosecutors argue he should be executed because he lied about the 9/11 plot. His defence say he knew very little.
Moussaoui has pleaded guilty to six counts of conspiracy to attack the US.
In order to deem him eligible for the death penalty, the jurors had to agree that Moussaoui's actions led directly to at least one death on 11 September 2001.
He was detained three weeks before the attacks but is accused of concealing the plot from FBI agents.
The sentencing trial now enters a second phase - expected to take several months - in which testimony will be heard from relatives of people who died in the terror attacks.
The jury must then retire for a second time to consider whether to impose the death penalty.
The BBC's Justin Webb in Washington says the prosecution will use the testimony from victims' relatives to try to press the case for execution.
Meanwhile, the defence will try to show Moussaoui is mentally ill, our correspondent says. It may also suggest that he wants to be executed - making the alternative penalty, life in prison, a tougher punishment.
Court official Edward Adams read out the jurors' verdict outside the Virginia courthouse.
The jury had found unanimously that the government had established beyond reasonable doubt that Moussaoui was guilty of "conspiracy to commit acts of terrorism", he said.
The jurors also decided that charges of conspiracy to destroy aircraft and conspiracy to use weapons of mass destruction had been proven, he said.
"By this verdict, the jury has found that death is a possible sentence in this case," Mr Adams concluded.
'Deserves to die'
Speaking outside the court, Rosemary Dillard, whose husband Eddie died in the 11 September attacks, said she believed Moussaoui deserved the death penalty.
"It's not just about my husband, it's what he did to the United States," she said.
"He did that to all of you. None of you feel the same way that you did before 9/11 2001."
Abraham Scott, whose wife Janice Marie died in the attacks, said he had found little comfort in the jury's decision. "I thought I'd be elated but I wasn't," he said.
"I describe him like a dog with rabies that cannot be cured. The only cure is to put him or her to death."
Senate Majority Leader Bill Frist welcomed the jury's finding as "a small but important piece of justice".
The US Justice Department said it was pleased with the result.
"Our efforts on behalf of the victims of 9/11 will continue as we pursue the next phase of this trial," a spokeswoman said.
In their closing arguments last Wednesday, prosecutors said Moussaoui was eligible for the death penalty because by lying about the 9/11 plot to FBI investigators, he contributed to the deaths of nearly 3,000 people.
They cited testimony from Moussaoui during the trial in which he said he was supposed to have flown a fifth plane into the White House on 11 September.
But lead defence lawyer Edward MacMahon described his client, a Moroccan-born French citizen, as a fantasist and al-Qaeda "hanger-on" who was trying to write himself a role in history.
Moussaoui was arrested on 16 August 2001 on immigration charges after the instructor at the flying school he was attending in Minnesota became suspicious of his behaviour.
He told federal agents he was a tourist who wanted to learn to fly for personal enjoyment.
He is the only person to be charged in connection with the 11 September 2001 attacks on New York and Washington.