Mohammed is expected to appear in court with Walid bin Attash, Ramzi Bin al-Shibh, Mustafa Ahmed al-Hawsawi and Ammar al-Baluchi.
The five men are charged with terrorism, hijacking aircraft, conspiracy, murder in violation of the law of war, attacking civilians, attacking civilian objects, intentionally causing serious bodily injury and destruction of property in violation of the law of war.
They face the death penalty if convicted of the most serious charges.
Siblings of Stephen Russell, a firefighter who died when one of the World Trade Center towers collapsed, told CNN on Friday that they favor a similar end for Mohammed.
"It has to be the death penalty," Chris Russell said in an interview in Guantanamo, where he and his sister Christina had traveled to watch the proceedings. "It doesn't have to be an ugly death. You can select what you wish off the menu."
"Life in prison drags it out and it costs the U.S. government money," said Christina Russell. "And it just lingers in the back of your head that these people are still alive ... it would bring closure."
But opponents of the military commissions for these cases say the suspects could benefit from not having hearings in federal court. "There's no precedents at all to rely on; this is sort of make it up as you go," Guter said. Since there are no precedents for many of the issues that could arise in the trial, any one of them could result in a conviction that could be overturned on appeal. Had the trial been held in federal court, those issues could have been settled long ago.
Guter said he believes that the victims and their families could pay the price for the cases being heard by a military commission. "One of the things you want to see is closure and finality, and I think ... if you were in the federal system, you'd get to finality faster. This is a risky way to take care of these trials, these important trials."