GUANTANAMO BAY NAVAL BASE, Cuba — Three of the five men charged with plotting the Sept. 11, 2001, attacks skipped their military tribunal hearing Tuesday after a judge ruled the men could not be forced to attend the session.

Khalid Sheikh 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.