martha raddatz tonight. thank you. and as this nation prepares to mark 20 years since 9/11, tonight, a hearing for the alleged mastermind and four accused conspiratconspirators. part of their defense, interrogation methods that were used. but this is finally under way, after years of delays. abc's senior national correspondent terry moran listening in on that hearing today. >> reporter: tonight, nearly 20 years after the attacks on 9/11, the long wait for justice continues. the pretrial hearing beginning today at guantanamo bay for five men accused in the plot that killed nearly 3,000 people. the lead defendant khalid sheikh mohammed, called "the principal architect of the 9/11 attacks" in the 9/11 commission report. ksm, as he was dubbed by the agents who tracked him down, was captured in pakistan in 2003. in 2007, he confessed in a statement to the combatant status review tribunal, saying, "i was responsible for the 9/11 operation, from a to z." but before the trial begins, the