In addition to those watching in Guantanamo, families and the public were invited to view the proceedings from closed-circuit video in New York, New Jersey, Massachusetts and Maryland.
Just seven families attended the first day of the hearings at a U.S. military base in Brooklyn. Ken Fairben came with a picture of his paramedic son, Keith. As he watched the proceedings, he said he looked into each of the men's faces, wondering, "What is he thinking? Why would he want to do this?"
The suspects could be sentenced to death if convicted, but Fairben said he hopes they get life sentences instead.
"If you give them death penalties, that's martyrdom to them," he said. "Why give them something they want?"
The focus of the week's hearing include broad security rules for the case, including measures to prevent the accused from publicly revealing in testimony what happened to them in the CIA prisons. Prosecutors have asked the judge to approve what is known as a protective order intended to prevent the release of classified information during trial.
Lawyers for the defendants say the rules, as proposed, will hobble their defense. The American Civil Liberties Union, which has filed a separate challenge, says the restrictions are overly broad and would improperly keep the public from hearing the men speak about their captivity.
The U.S. government has acknowledged that the defendants were subjected to "enhanced interrogation techniques" before being transferred to Guantanamo in 2006, which in some cases included the simulated drowning method known as waterboarding.
Mohammed and his four co-defendants face charges that include terrorism, conspiracy and 2,976 counts of murder in violation of the law of war, one count for each known victim of the Sept. 11 attacks at the time the charges were filed.
Mohammed, a Pakistani citizen who grew up in Kuwait and attended college in North Carolina, has told military officials that he planned the Sept. 11 attacks "from A to Z" and was involved in about 30 other terrorist plots. He has said, among other things, that he personally beheaded Wall Street Journal reporter Daniel Pearl. In addition to Binalshibh and al-Aziz Ali. the other defendants are Walid bin Attash; Mustafa Ahmad al-Hawsawi.
Associated Press writer Verena Dobnik contributed to this report from New York.