▶ Watch Video: 9/11 families outraged over potential plea deals for terror attack orchestrators

On the 21st anniversary of 9/11, CBS News has confirmed that military prosecutors and attorneys for five defendants charged for their roles in the attacks are negotiating potential plea deals that could take the death penalty off the table and keep the detention camp at the military base in Guantánamo Bay, Cuba, open for the foreseeable future.

Their cases have stalled over access to CIA evidence and, more recently, delays caused by the COVID-19 pandemic.

The chief defendant is Khalid Sheikh Mohammed, the self-described architect of 9/11. The other four defendants are Ramzi Binalshibh, Mustafa Ahmed al-Hawsawi, Walid bin Attash and Ammar al-Baluchi.

The possibility of a plea deal has angered the families of some 9/11 victims, including Debra Burlingame, whose brother, pilot Charles “Chic” Burlingame, was killed when al Qaeda terrorists took over his plane, American Airlines Flight 77, and crashed it into the Pentagon.

“We didn’t have remains for weeks,” his sister Debra Burlingame told CBS News. “We were constantly saying to each other, ‘What would Chic want? What would Chic do?'”

Burlingame said she has been in touch with other 9/11 families.

“The families are outraged,” she said of the possibility of plea deals. “They don’t want closure, they want justice.”

Another group, 9/11 Families for Peaceful Tomorrows, has said that a guilty plea and agreement not to appeal the sentence “would be partly in recognition of the torture each of the defendants experienced” and bring “some measure of judicial finality.”

“All five defendants and the government are all engaged in good faith negotiations, with the idea of bringing this trial which has become a forever trial to an end,” said James Connell, a defense attorney for al-Baluchi.

“Mr. al-Baluchi’s number one priority is obtaining medical care for his torture,” Connell continued. “In order to get that medical care, he is willing to plead guilty to a substantial sentence at Guantanamo in exchange for a guarantee of medical care and dropping the death penalty.

Before their transfer to Guantanamo Bay in 2006, the five 9/11 defendants were held by the CIA and interrogated. Critics call the extreme interrogation tactics torture.

“The one that has had perhaps the most lasting physical impact was what they called ‘walling,'” Alka Pradhan told CBS News. Pradhan is a human rights attorney on the al-Baluchi legal team.

“He had told us that his head was bashed against a wall repeatedly until he saw sparks and fainted,” Pradhan said. ” The result of that is, as we’ve had several medical experts examine him, is lasting brain damage .”

When asked by CBS News if declining to pursue the death penalty was fair, Pradhan responded, “The United States government failed all of us after Sept. 11 in their decisions to use illegal techniques and illegal programs … In doing so, it rather corrupted all the legal processes.”

A spokesperson for the military trials did not answer CBS News’ questions about the 9/11 case but confirmed that “the parties are currently engaged in preliminary plea negotiations,” pointing to recent court filings.

Asked if there can be justice without consideration of the death penalty, Burlingame said no. “I will not have closure as long as there is any possibility for some future president to commute their sentences or trade them away for something political that they want from some other country.  That’s a very real possibility because it’s now been done over and over and over again.”

Burlingame said her fear now is that “we’ve reached a point in our country where we just don’t seem to have … the courage of our convictions.”

Her brother, Chic, was laid to rest at Arlington National Cemetery. Asked if forgiveness is possible, Burlingame said, “Yes, but not for them … You have to truly take responsibility for what you’ve done. And they will never do that.”