You may or may not buy it, but it's worth reading just to see the case made. Basically, the argument is that Bin Laden is an active military target, though it gets more detailed than that.
When using lethal force within a field of combat, the military’s Rules of Engagement have historically defined two kinds of acceptable targets. The most common are known as “combat-based targets.” In a long article that I wrote for The New Yorker in 2009, titled “The Kill Company,” I described them as:
People who act in a hostile manner or display hostile intent. Hostile actions are easy to identify. (If a cabdriver fires a rifle at a soldier, he instantly becomes a combatant.) Establishing hostile intent is harder. (If a cab is racing toward a soldier, is the driver’s intent hostile, or is he drunk?) Whenever a soldier uses force, the rules say, his reaction must be proportional to the threat. In part because judging intent and proportionality are subjective, the Army scrutinizes every incident in which one of its weapons is discharged.
Had bin Laden been armed and shooting at the time of the raid, he would have very easily met the standard of a combat-based target, and could legally have been killed. But as Jay Carney, the White House spokesperson, said the other day, “Resistance does not require a firearm.” Bin Laden could have been legally killed if he were holding a weapon and not firing—or if he were holding no weapon at all. Any soldier seeing bin Laden and recognizing him could make a reasonable assumption that he had “hostile intent.” After all, Al Qaeda bodyguards were nearby, and they were shooting at the Navy SEALs to defend him. “This is a guy who’s extremely dangerous,” John B. Bellinger III, legal counsel at the National Security Council and State Department in the Bush Administration, told the New York Times. “If he’s nodding at someone in the hall, or rushing to the bookcase or you think he’s wearing a suicide vest, you’re on solid ground to kill him.” Military law tends to recognize that soldiers must confront myriad, and potentially lethal, ambiguities amid the heat of battle.
That being said, the legality for killing bin Laden is not especially dependent upon his behavior during the raid because, in his case, an alternate (and more relevant) aspect of the Rules of Engagement applies. There is no military circumstance where an Al Qaeda operative of bin Laden’s stature could merely be a “combat-based target” in the way a low-level insurgent at a roadside checkpoint would be, because he is also a high-value target, and his status as such matters. In 2009, I also described why:
For many years, soldiers have also been permitted to kill people because of who they are, rather than what they are doing—such people are “status-based targets.” During the Second World War, an American infantryman could shoot an S.S. officer who was eating lunch in a French café without violating the Law of War, so long as he did not actively surrender. The officer’s uniform made it obvious that he was the enemy. In Iraq, the R.O.E. listed about two dozen “designated terrorist organizations,” including Al Qaeda, and, if it can be proved that someone is a member of one of these groups, that person can legally be killed. For a time, the R.O.E. designated as a status-based target any armed man wearing the uniform of the Mahdi Army—the militia led by Moqtada al-Sadr. (After Sadr called a truce, in 2004, the militia was provisionally taken off the list.) But most insurgent groups in Iraq don’t wear uniforms, so their members must be “positively identified” by informants or other forms of intelligence before they can legally be killed. An insurgent is positively identified if there is “reasonable certainty” that he belongs to a declared hostile group.
What was true in Iraq and in the Second World War also applies in the ongoing conflicts in Afghanistan and Pakistan. Targeted air strikes are status-based operations. The drone strikes are status-based operations. Raids conducted by Special Forces to kill key militants—as in the case of Abu Musab al Zarqawi, who was killed in Iraq by Special Forces working under the command of General Stanley McChrystal—are status-based operations. A status-based target can become a non-combatant (that is, illegal to kill) only if he is wounded to the point where he no longer poses a threat, or if he is in the process of surrendering. This is why Eric Holder said, during a recent Congressional hearing, that if bin Laden “had surrendered, attempted to surrender, I think we should obviously have accepted that, but there was no indication that he wanted to do that, and therefore his killing was appropriate.” In such a circumstance, the law suggests that the onus is on the target to immediately revoke his combatant status. Soldiers do not have to wait.