GUANTANAMO BAY NAVAL BASE, Cuba - Almost seven years after terrorists hijacked airliners and used them as missiles to kill 2,973 people, five men who allegedly plotted the attacks face a military tribunal today.

Khalid Sheikh Mohammed, the confessed mastermind of the Sept. 11 attacks, will be arraigned simultaneously with four other detainees inside a high-security courthouse at the U.S. Navy base at Guantanamo Bay, Cuba.

Mohammed boasted of numerous attacks and plots against the United States in a closed military hearing last year. The al-Qaeda kingpin and his confederates will be given the chance to speak out again in their war-crimes trial, according to a top tribunal official, Air Force Brig. Gen. Tom Hartmann.

"In the course of trial they'll have opportunity to present their case, any way they want to present it, subject to rules and procedures," Hartmann said in an interview. "That's a great freedom and a great protection we are providing to them. We think . . . it is the American way."

Attorney General Michael B. Mukasey also said the tribunals would be "in the best traditions of the American legal system" even though the military judges can consider hearsay evidence and confessions obtained through coercion, which are not admissible in civilian courts. "Different situations call for different solutions," he said.

The arraignment will launch the highest-profile test yet of a tribunal that faces an uncertain future.

The U.S. Supreme Court struck down an earlier system as unconstitutional in 2006, and is to rule this month on the rights of Guantanamo prisoners, potentially delaying or halting the proceedings.

With less than eight months remaining in President Bush's term, presidential candidates Barack Obama and John McCain both say they want to close the military's offshore detention center.

Dozens of U.S. and international journalists arrived at Guantanamo yesterday on a military plane from Andrews Air Force Base outside Washington, joining prosecutors, defense attorneys and observers who arrived earlier.

Mohammed and the four alleged coconspirators all face possible death sentences.

Family members of those killed on Sept. 11, 2001, wanted to attend, but the military said it was too difficult logistically to accommodate dozens more people.

Instead, the military is planning to show the trial, but not the arraignment, on closed-circuit television to victims' families gathered on U.S. military bases.

"For transparency and to add legitimacy to the trial, they should have the loved ones there," said Dominic J. Puopolo, whose mother, Sonia Morales Puopolo, was a passenger on American Airlines Flight 11, the first jet that crashed into the World Trade Center.

Puopolo said he also wanted to see the defendants, especially Mohammed, who claimed he proposed the plot to Osama bin Laden.

"This is an architect of such pure evil," Puopolo said. "I want to see him eye to eye."

The tribunals, which Congress and the Bush administration resurrected after the 2006 Supreme Court ruling, have been mired in confusion over courtroom rules and dogged by delays.

No detainee has been tried yet, although David Hicks was convicted through a plea bargain and served a nine-month sentence in his native Australia.

Critics say men accused of such horrific crimes must be brought to justice, but in a way that shows the world that they are treated fairly.

"While everyone seems to recognize that the time to bring those responsible for 9/11 to justice is long overdue, this needs to be done in a system that has credibility," said Jennifer Daskal of Human Rights Watch.

The four defendants due to appear with Mohammed are: Ramzi Binalshibh, said to have been the main intermediary between the hijackers and al-Qaeda leaders; Ali Abd al-Aziz Ali, known as Ammar al-Baluchi, a nephew and lieutenant of Mohammed's; Baluchi's assistant, Mustafa Ahmad al-Hawsawi; and Waleed bin Attash, a detainee known as Khallad, who allegedly selected and trained some of the 19 hijackers.