Terrorists are the worse kind of criminals. They deserve no due process. Instead of Guantanamo Bay style prisons and the long drawn out process of legal shenanigans, when terrorists are caught, the punishment should be instant.
Nine grams of lead in the back of the head is much cheaper than interminable trials and incarcerations. It is more efficient than execution by lethal injection, the rope or the electric chair.
It is also the terrorists' own way of doing their dirt. An eye for an eye.