The main suspect in the bombing of the USS Cole warship has appeared before a judge after nearly a decade of confinement at various clandestine CIA prisons and Guantanamo Bay.
Saudi-born Abd al-Rahim al-Nashiri, 46, faces the death penalty for allegedly planning and preparing the October 2000 attack on the US navy destroyer in Yemen's port of Aden that killed 17 sailors and wounded 40.
In a top-security courtroom at the Guantanamo Bay US naval base in Cuba, he postponed entering a plea and waived the reading of war crimes charges that include murder, attempted murder, conspiring to commit terrorism and attacking civilians.
It was the first public appearance in years for a "terror" suspect who has been essentially invisible since his 2002 capture in the Gulf and subsequent incarceration.
The trial was the first since Barack Obama, the US president, approved the resumption of military trials for detainees held at Guantanamo Bay.
The proceedings end a two-year ban on military tribunals at Guantanamo and was the latest acknowledgement that the prison Obama had promised to shut down within a year of taking office will remain open for some time to come.
The Pentagon believes Nashiri bought the small boat and explosives used in the Cole attack.
"By torturing Mr Nashiri, the United States has lost all moral authority to try Mr Nashiri."
Richard Kammen - Defence Lawyer
Nashiri is also accused of involvement in a January 2000 attempted attack against another US warship in Aden, the USS The Sullivans, and a French oil tanker near Yemen.
Along with five men accused of orchestrating the attacks of September 11, 2001, Nashiri is among the "high-value detainees" held by the US, and could be the first terrorism suspect sentenced to death by a military court under the Obama administration.
In 2004, a Yemeni court had charged Nashiri and five others for carrying out the attack.
Nashiri was captured in Dubai in 2002 and held in secret CIA prisons before being sent to Guantanamo in 2006.
The CIA acknowledged destroying videotapes of interrogations, during which he was stripped naked and hooded while a gun was loaded and a power drill revved next to his head.
He also was subjected to "waterboarding," which creates the sensation of drowning.
A congressional investigation also found that handlers loaded a gun and powered a drill near his head.
Nashiri has said he gave false confessions to make them stop abusing him.
'Lost all moral authority'
"By torturing Mr Nashiri the United States has really lost all moral authority to try to kill him," defence attorney Richard Kammen said outside the courtroom.
In court, Kammen asked the judge whether he considered torture to be a mitigating factor that might prevent Nashiri's execution, even if he is convicted of all the charges, noting Nashiri's case could be the first capital case to reach trial in the Guantanamo tribunals.
Mark Martins, the military commission's chief prosecutor, said that "no statement obtained as a result of cruel, inhuman or degrading treatment" would be accepted as evidence.
Such claims of torture by the defence team could complicate the trial and revive debate over the efficacy of the anti-terrorism strategy of Obama's predecessor, George W Bush.
Three trials have taken place at Guantanamo since Obama took office in January 2009, but those proceedings began under Bush.
In one of his first decisions as president, Obama froze proceedings at the Guantanamo military tribunal as part of his ultimately ill-fated promise to close the facility in southeastern Cuba within a year of entering the White House.