The terrorist attacks were an act of war. They were not a criminal act, and we shouldn't try to achieve justice through courts of law.
Osama bin Laden and those who adore him do not believe in the Western system of justice. It is impossible practically by definition for a Western court to provide a fair trial to someone who doesn't believe in Western courts. In what sense would Osama bin Laden acknowledge a guilty verdict as just? He would not, and nor would those who adore him. It would be a travesty to put him on trial, a propaganda play.
Government gains its legitimacy from the consent of the governed. Bin Laden doesn't acknowledge the legitimacy of Western courts. It makes no sense to treat him as a member of the global community who has broken the community's laws. He is instead an outsider from the West. He did not commit crimes against his fellow people. He committed acts of war against his enemy.
He is trying to kill the West. The West should kill him first.
If he surrenders, then he'll be a prisoner of war, and we'll put him on trial for war crimes. But it makes not sense to go after him as if he were a criminal.