Guantanamo detainee Abu Zubaydah is expected to give information about his torture at the hands of the CIA, after he was detained following the 2001 Al Qaeda attacks on the United States.
Pre-trial hearings are continuing for five Guantanamo Bay detainees accused of plotting the 9-11 attacks, who've been held for nearly 16 years.
9-11 refers to the September 11, 2001 attacks by the Al Qaeda terrorist group on the United States, which killed almost 3,000 people, injured more than 6,000 others, and caused at least $10 billion in property and infrastructure damage, with an estimated $3 trillion in total costs.
The court is scheduled to hear testimony on Friday from Abu Zubaydah, who has been held in the facility's secretive "Camp 7" prison for 15 years without charge.
Abu Zubaydah is expected to give up his right to immunity in order to give evidence about the conditions at the camp, which is said to be one of the most secure prisons in the world.
Very little is known about the camp, which houses the five defendants.
Khalid Sheik Mohammed, the alleged architect of the 9-11 attacks, is also among the five men.
Harry Horton is in Cuba where he is following the hearings for TRT World.