GUANTANAMO BAY NAVAL BASE, Cuba -- Three of the five men charged with plotting the Sept. 11 attacks skipped their military tribunal hearing Tuesday after a judge ruled the men could not be forced to attend the session.

Khalid Sheik Mohammed, the self-professed 9/11 mastermind, was absent as attorneys delved into a dense debate on legal motions, including rules for handling classified evidence at trial.

Mohammed was taken from his cell at the U.S. base in Cuba to a holding cell outside the courtroom, then chose to boycott at the last minute. He gave no reason for wanting to sit out the hearing.

Saudi defendant Mustafa Ahmad al-Hawsawi and Pakistani national Ali Abd al-Aziz Ali, a nephew of Mohammed, also chose to boycott the hearing.

Those who showed up in court, for the second day in a weeklong pretrial hearing, were Walid bin Attash, a Yemeni who grew up in Saudi Arabia, and Ramzi Binalshibh, another Yemeni who was originally chosen to be one of the hijackers but couldn't get a U.S. visa to enter the country.