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 Thursday. 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 remote U.S. Navy base in Guantanamo Bay, Cuba. Mohammed boasted of numerous attacks and plots against the United States in a closed military hearing last year, and the al-Qaida 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 told The Associated Press. “That’s a great freedom and a great protection we are providing to them. We think ... it is the American way.”

The arraignment will launch the highest-profile test yet of a tribunal system 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.