I'm sorry but that is just not rational. He may have been a dead martyr but now he is a live martyr. He will be celebrated as the one that America was afraid to kill. Here's the truth, he should have been sentenced to death just as a rabid dog is sentenced to death. The country is not better off because we were "fair" to this animal, in fact, to use the logic the jury used i.e that he did not physically act on 911 then the same logic would apply to Osama Bin Laden. I shudder to think what would happen should OBL ever stand before an American jury.
I hear what you are saying and for the average jihadi I wish we wouldn't even spend the bullet but stretch their neck.
My first instinct was to behead this waste. But after I thought of it, death is too easy for him. A life in solitary has got to be hell on this earth. 6 x 6 brick wall cell,3 meals of bread and water, table, chair, koran and a piece of rope. When he decides he's had enough, he'll figure it out.
As for OBL, it doesn't follow my above thinking but, I would saw his head off with a rusty butter knife on live TV.