I think he should be locked up and prevented from communicating with the outside world, so that he can't continue to direct terrorists to commit terrorist acts.

edit: Note that I didn't intend for this to turn this into a discussion for/against the death penalty. I just wanted to point out that, as a nation, we have a certain amount of bloodlust that's closely tied to our patriotism. That's the only reason we've been able to stomach the wars in the middle east with the losses of our countrymen. I wish everyone on the planet were able to suppress those feelings and deal logically and calmly with everything, instead of making war upon each other.