The accused mastermind of the Sept. 11 terror attacks is facing a military judge in his long-awaited first public appearance before a war-crimes tribunal.

Khalid Sheikh Mohammed and four alleged co-conspirators have taken their seats at defense tables before Judge Ralph Kohlmann, a Marine colonel.

Their arraignment Thursday is the highest-profile test yet of the controversial tribunal system, which is being challenged in court. It comes seven years after the attacks. All five face the death penalty if convicted.