Family members of one of the 3,000 victims who died in the Sept. 11, 2001, terror attacks are still wondering 20 years later when a verdict will be determined in the case of accused 9/11 planner Khalid Sheikh Mohammed.

Retired U.S. Air Force Lt. Col. Don Arias watched the beginning of Mohammed's trial from behind a thick pane of glass with his sister in 2009 at Guantanamo Bay in Cuba. He remembers attorneys arguing over whether the accused terrorist received the cushion he requested for a bus ride from prison to the courthouse, he told Fox News.

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"They started arguing about a cushion," Arias recalled. "Khalid Sheikh Mohammed's lawyer said that he had asked for a cushion for the van ride from the detention center to the courtroom, and he had not received that question. The government said, ‘Yes, he had been provided a cushion,’ and then they went back and forth arguing about a cushion for the van ride. And my sister looks at me and says, '3,000 people dead, and they're arguing about a cushion.' And she got up and walked out."

Arias and his sister, Lorraine, lost their brother, Adam, on 9/11, when he died trying to help people out of the World Trade Center's south tower, where he worked on the 84th floor. Lorraine has also since died of COVID-19. Mohammed has survived both siblings.

USAF Ret. Lt. Col. Don Arias and his sister, Lorraine, lost their brother, Adam, on 9/11, when he died trying to help people out of the World Trade Center's South Tower, where he worked on the 84th floor at the time.

USAF Ret. Lt. Col. Don Arias and his sister, Lorraine, lost their brother, Adam, on 9/11, when he died trying to help people out of the World Trade Center's South Tower, where he worked on the 84th floor at the time. (Credit: Don Arias)

The alleged 9/11 planner and four other Gitmo detainees appeared together in court Tuesday for the first time in 500 days for pretrial headings after delays brought on by the coronavirus pandemic. The hearings, which resumed Wednesday, nearly 20 years after the attacks, are the latest attempt to advance a case that has been bogged down for years amid legal challenges

Arias described his brother, whom he said he talked to almost every day when he was alive, as a "wonderful guy" who believed in "prosperity and good work."

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"All the guy wanted to do was get on with his life, and he gets caught up in this war because we've got some crazy stuff that some crazy people in the world [think] who call themselves al Qaeda, which, of course, morphs into other things. The Haqqani network and Taliban – they're all the same, quite frankly. And now we've got 3,000 dead people," he said.

Arias recalled calling his brother after watching the north tower struck and telling him to come home. 

Adam Arias (right) pictured with his brothers and father (Credit: Don Arias)

Adam Arias (right) pictured with his brothers and father (Credit: Don Arias) (Don Arias)

"Knowing what I knew, which was very little at the time, my last words to him … I said, ‘Go home,'" the Air Force veteran said. " … And later my brother was killed when Tower 2 fell down. … He had hung around to assist people ... So, you know, he died with his boots on. I was very proud of the way he lived, and in a strange and funny way, at least, I'm proud of the way he died because he died in the service of other people."

To speed up the trial, the veteran suggested officials involved in the case stay at Gitmo during the proceedings to eliminate travel inconveniences that rack up time and heavy costs. Families are tired of waiting for a trial and a verdict, he said.

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Mohammed and his four other co-defendants are charged with several crimes, including terrorism, hijacking and 2,976 counts of murder for their alleged roles in planning and providing logistical support to the Sept. 11 plot. 

USAF Ret. Lt. Col. Don Arias and his sister, Lorraine, lost their brother, Adam, on 9/11, when he died trying to help people out of the World Trade Center's South Tower, where he worked on the 84th floor at the time. (Credit: Don Arias)

USAF Ret. Lt. Col. Don Arias and his sister, Lorraine, lost their brother, Adam, on 9/11, when he died trying to help people out of the World Trade Center's south tower, where he worked on the 84th floor. (Credit: Don Arias) (Don Arias)

The quintet have been held at Guantanamo Bay since September 2006 after several years in clandestine CIA detention facilities following their capture.

Air Force Lt. Col. Matthew McCall, the latest and seventh different judge assigned to the case, said on Wednesday in the courtroom that the death penalty is a "valid option" for the five 9/11 prisoners and that he "can be a fair judge."

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Arias said those involved in the military tribunal and Mohammed's case "can't forget" the almost 3,000 U.S. citizens killed on 9/11 as the nation approaches 20 years since the attacks.

"We just can't forget people. … And we say, ‘Oh, never forget,' … but we have forgotten. Moreover, we don't give a damn anymore, as evidenced by our exit from Afghanistan," he said. "So I don't want to hear ‘never forget’ from any of this administration at all."

Fox News' Lucas Tomlinson and Vandana Rambaran contributed to this report, as well as the Associated Press.