As the trial of Zacarias Moussaoui, dubbed the would-be "20th hijacker" of 11 September, got under way in Virginia, relatives of the 3,000 or so victims expressed their anger towards the attackers.
The parents of WTC victim Glenn Kirwin watched the trial in New York
In some cases, they also criticised the authorities they felt had let them down.
Sally Regenhard, who lost her firefighter son Christian, was one of the 500 relatives who chose to watch the trial on closed-circuit television.
"After four and a half long years, this is our only attempt to get a scintilla of justice," she told the Associated Press at a courtroom showing the video link in New York.
"What does accountability feel like? That's what eluded the families of the victims. They [the hijackers] all got away with murder so we only have him [Moussaoui] left."
Barry Zelman, whose brother Kenneth died at the age of 36 in the World Trade Center, was also at the New York courtroom, near where the WTC once stood.
Moussaoui, he said, was "al-Qaeda in the flesh". "There's going to be a lot of anger, a lot of emotion," he added.
'Too much pain'
William Doyle lost his son in the attack on the WTC and decided to come to Virginia in person to watch the actual trial.
While he wanted to "confront" Moussaoui, he told the AFP news agency, he also wanted to see anyone guilty of negligence punished.
"I'm concerned that there's only one person that's being tried and I'd like to see all the people that failed us being held accountable," he said.
Christine Huhn, who lost her husband, said she had decided not to watch the trial.
"It just probably would make me angry because the government had him in custody and they really didn't do anything to investigate him before 9/11," she said.
"I didn't really feel like the FBI had their act together."
Kurt Horning, who lost his son Matthew, said he had absolutely no desire to see the trial.
"What happens to Moussaoui is out of my hands and I really don't want to justify his existence by showing up," he said.
"I've suffered enough pain. If I want more I'll just hit myself over the head with a hammer."