Relatives who were chosen by lottery have travelled to Cuba for arraignment of Khalid Sheikh Mohammed and others
Relatives of those killed in the 9/11 attacks will see the plot's alleged mastermind Khalid Sheikh Mohammed and four other men charged at a military tribunal at Guantánamo Bay.
Six victims' families, chosen by lottery, have travelled to Guantánamo to see the arraignment of Mohammed, Ramzi bin al-Shibh, Ali Abd al-Aziz Ali, Mustafa Ahmed al-Hawsawi and Walid bin Attash, nearly 11 years after the 2001 attacks.
The former chief US prosecutor at Guantánamo Bay has strongly denounced the military trial in which the men will face charges of 2,976 counts of murder, as well as terrorism, hijacking, conspiracy and destruction of property. The prosecution is seeking the death penalty for all of the men.
Other relatives of the victims will watch the trial via closed-circuit TV.
"I want to bear witness that in fact these people are brought to justice," said Al Santora, whose son Christopher, a firefighter, died at the World Trade Centre.
Santora and his wife, Maureen, plan to watch Saturday's arraignment at Fort Hamilton in Brooklyn, one of the military bases where the proceeding will be broadcast live for victims' family members, survivors and emergency personnel who responded to the attacks.
The military trial has been criticised by Morris Davis, former chief US prosecutor at Guantánamo, who said the proceedings were intended primarily to prevent the defendants from presenting evidence of torture.
Davis said the military commissions will be badly discredited by the use of testimony obtained from waterboarding and other "enhanced interrogation" techniques used on the accused men.
The former colonel, who resigned over the issue, wanted to see Barack Obama follow through on a commitment to move the trials to more open civilian courts. He said, however, that advocates of military tribunals prevailed in large part because the rules of evidence prevent the defendants from giving detailed descriptions of how they were tortured. They are also prevented from revealing other sensitive information such as details of the CIA's secret detention programme and the co-operation of foreign countries, such as Britain, in their capture and interrogations.
"The truth is the reason the apologists want a second-rate military commission option is because of what we did to the detainees, not because of what the detainees did to us," Davis said. "If you look beneath the layers on why there's even an argument for military commissions, it's really about our mistreatment of detainees – a fairly small number of people for a short period of time that because of what most people would call torture, it makes it a greater challenge to prosecute the cases in our regular courts."
Other senior military lawyers have objected to the trials, including Rear Admiral Donald Guter, the former judge advocate general of the navy, who called the Guantánamo commissions a "circus".
This weekend's hearing will be the second attempt to try Mohammed. At a similar hearing in 2008, he tried to plead guilty, saying he wanted to be put to death as a martyr, but the US supreme court later struck down the rules of evidence and the trial was called off.
The president did oversee important changes to the conduct of the military trials including new rules that do not allow a defendant's own confessions under torture to be used against him. But the statements of others who were tortured can be used, which permits the interrogations of the five accused to be used against each other.