The Pentagon has cleared the way for a death penalty trial against five Guantanamo Bay inmates charged with engineering the 11 September 2001 terrorist attacks on the United States.
Retired navy vice admiral Bruce MacDonald, who is in charge of military commissions, has signed off on the capital trial against alleged mastermind Khalid Sheikh Mohammed and four accused co-conspirators.
The other four men facing the death penalty charges are from Yemen, Saudi Arabia and Pakistan.
They all face charges in the system set up by former president George W. Bush within months of the attack, and then modified by President Barack Obama in 2009.
It will be up to an 11 member team of US prosecutors to prove the charges to a military jury of a dozen or more members.
If convicted, the five could be sentenced to death.