Fortunately Obama is a lot smarter than you are.
The smarter the better. He's the president, you know.
Evidence suggests bin Laden was unarmed, did not go for a weapon, and was in a house surrounded by SEALs. So effectively he was already captured. Killing a captive who poses no immediate threat is a crime under military law as well as all other law.
You really expect to sell that noise to me? You might as well be peddling a cart of goat manure.
bin Laden was the leader of an organization that specializes in suicide bombings and booby-trapping themselves, whose members, including the venerable bin Laden, are known to wear bomb vests. bin Laden even published his longings for martyrdom. Those Seals would have looked pretty stupid if they'd gotten themselves and their team blown away by bin Laden because they didn't have the good sense to shoot the crazy bastard on sight, resulting in the total failure of the mission.
The Seals' responsibilities were to the mission, their team, and themselves. Screw the enemy.
Which is most likely why Obama has kept details of bin Laden's death deliberately vague. Doing so makes it impossible to answer the question of legality with certainty.
"the question of legality" exists only in the minds of obsessive finger-pointers. Soldiers are not required to unnecessarily expose themselves to enemy fire, grenades, bombs, booby traps, etc, solely for the purpose of attempting to capture an inherently dangerous enemy.
If bin Laden wanted to surrender, he should have halted and put up his open hands immediately. He should not have retreated into the darkened room containing weapons. Retreat is not surrender. Retreat is a combat tactic.
You can bet that if bin Laden had held a weapon, officials would have shouted from the rooftops how the SEALs tried to take him alive, but 'unfortunately' had to kill him in self-defense.
I very gravely doubt that. If I were the president, I would at least reprimand any official who spouted such dweezleblabber.
If bin Laden had been seen with a weapon in his hand, intelligent officials would have told the truth: that bin Laden was seen to be armed and was shot immediately by a Seal, rather than foolishly risking the mission, his life, and the lives of his team members.