Plane that hit the pentegon was supposed to hit either capitol or White House, but over shot due to lack of flying experiance. Boom, large building straight ahead.
He is probably telling the truth about the shoe bomber and himself. He did help set things up apparently.
As for death sentence, dump him in for LIFE with NO PARROLL, and then let him mingle with the inmate population. They may be criminals, but many if not most are very loyal to US and would finish the job. No martyrdom when you get an ice pick up your ass.