Utter Nonsense.
The Killing of Osama is perfectly legal under the laws that govern Armed Conflict. Osama and his lot Declared war on the US Openly and publicly. Not just with actions but with words. The US congress passed a resolution authorizing any and all means to neutralize the Threat posed by Osama and his organization. Nuff said.
Only under liberal logic, such as the kind Obama engages in all the time. The kind where you pretend this is not a war, and talk about handing out Miranda Rights and Trails to Enemy combatants in a war, could you fathom the idea that the killing of Osama could be illegal.
Ironic eh.
This was not some common Criminal, and he was not the Head of an Organized Criminal Enterprise. Osama was the Commander and Chief of an army that had Publicly Declared war on the US and inflicted mass Casualties to Civilians. Only a complete Idiot would say it is Illegal for a Nation to Target and Kill the Leader of an enemy Army it was at war with. Sheer Stupidity.