Bin Laden admitted his guilt so there wasn't any need to prove his guilt. Where exactly would one find a "jury of his peers"? I am pretty sure if we knew where they were they wouldn't be available for a court date. Where would you go to find someone who has never heard or read about Bin Laden? How could you possibly imprison Bin Laden? Some kooky bunch of terrorists would kidnap some hostages and then want to negotiate his release and the US doesn't negotiate with terrorists.
Seriously, folks need to get a grip on the fact that sometimes there are circumstances outside the norm and there is no playbook. There is a war on terror...or so the Bush administration tried to tell us. In war people get killed. It isn't pretty and it isn't "fair". It's war. Our government did what needed to be done.