Why did the United States choose to launch a raid against al-Qaeda leader Osama bin Laden's compound in Abbottabad, Pakistan, rather than bombing it? It wasn't because of a "law enforcement mindset." And it wasn't compelled by human rights law. Rather, it was the best option based on the military objectives, available intelligence, and the law of armed conflict. 

On the one hand, practical considerations dictated this riskier kind of raid. The United States needed to have a body to prove, once and for all, that the hard-to-kill bin Laden was in fact dead. The recent media fascination with whether the U.S. will release photos of his body lends credence to this concern.

A second issue prompting the raid was that the Obama administration was worried about collateral damage. This problem is more serious than some may initially suspect. Abbottabad is a heavily populated city, with nearly 1 million residents. Moreover, numerous civilian residences and the Pakistani military academy were near bin Laden's "drone-proof compound." There's little doubt that the risks to nearby residents certainly weighed on the minds of senior policymakers and President Obama. The matter of collateral damage alone, though, may not have been enough to tip the scales away from a bombing operation.

Instead, the issue may have been the uncertainty over whether bin Laden was even in the compound. Nation-states are simply not permitted to  drop bombs in the hope they will kill the right person; they need to be reasonably certain they are attacking the right target. That fact leads us to the legal concerns that may have necessitated a raid rather than a bombing operation.

The Requirement to Positively Identify a Target

Most contemporary discussions of collateral damage skip the threshold legal question likely posed by the Obama administration, namely whether bin Laden or some other lawful military target was actually inside the compound. Unless that question could be answered to a reasonable degree of certainty, any bombing operation would have been unlawful, even with no or minimal collateral damage to surrounding persons and objects.

This reality flows from the principle of distinction, (or "positive identification" in U.S. military parlance) a fundamental tenet of the law of armed conflict. Armed forces are required to "at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives." Positive identification, according to U.S. policies, requires that commanders know with reasonable certainty that "a functionally and geospatially defined object of attack is a legitimate military target." In short, directing attacks against civilians (in this context, non-uniformed personnel) is not permitted, unless they are directly participating in hostilities.

This requirement closely tracks with the text of Protocol I Article 52(2), of the Geneva Conventions, which defines military objectives as "those objects which by their nature, location, purpose or use make an effective contribution to the military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage." This definition, by implication, includes enemy personnel as legitimate military objects. In the case of "civilians," such as bin Laden and those with him in his compound, this identification task also required that those civilians meet the requirement that they are "directly participating in hostilities." As al-Qaeda's leader, bin Laden would easily satisfy this definition, as would his bodyguards and couriers, if only they could be positively identified. 

If the U.S. cannot positively identify a lawful target, the law of war and U.S. policies instruct that no bombing operation can take place. This is not to say that the law of armed conflict requires perfection in positively identifying a target (look to America's ongoing CIA drone campaign in Pakistan to see examples of when mistakes have been made); rather, the drafters of the law of armed conflict intended these rules to be a guide to decision-making in warfare, and recognized that bright line rules and fixed borderlines between civilian and military objectives might be difficult to distinguish. However, in the case of uncertainty about identity, the law stands firmly in favor of presuming civilian status, hence the U.S. requirement of positive identification. Thus, the burden is on the attacker to exercise discretion and caution, and they are judged by whether they acted reasonably and honestly in the exercise of those responsibilities. 

The positive identification test does not involve any balancing of potential collateral damage against military advantage. Instead, the focus in this case would be on whether the target is a civilian directly participating in hostilities, whose killing furthers a definite military advantage. Of course, those concerned with collateral damage should not overlook the importance of the positive identification step, as its relationship to collateral damage cannot be overstated -- failed positive identification is, according to research I have conducted, one of the leading causes of collateral damage in current U.S. military operations .    

Applying the Requirement of Positive Identification to the bin Laden Operation

It turns out that the Obama administration was not particularly certain about bin Laden's presence at the compound. Recent reports suggest there was a 20 percent - 40 percent chance that he wasn't in the building. Granted, substantial circumstantial evidence suggested some high value target was in the compound -- but this was not the type of information that would lawfully permit a bombing operation anywhere, let alone one deep in the heart of Pakistan. 

Rather, what the law requires, and what the U.S. government needed, was a positive identification of at least some of the building's residents. Eventually one man, bin Laden's courier, was tracked to the compound. The intelligence community also believed that the courier's family, his brother's family, and an unknown third family that matched the description of bin Laden's family were also in the home. They even believed a tall man who never left the house was also inside. Tally it up and you have one positive identification - of the courier, not bin Laden -- and a building full of maybes. 

Realistically, President Obama and everyone else at the White House who considered the bombing option probably thought about the fact that bin Laden might have been in the compound. But that chance, as a matter of law, was simply not part of the calculus because he wasn't positively identified as being present. Thus, when the value of the courier (the only known target) was balanced against the likely collateral damage, the obvious conclusion was that a bombing mission could not take place. A contrary choice would have been a gamble, and that gamble takes place in a context of heavy scrutiny and criticism of U.S. counterterrorism policies by allies and various other groups. Those political realities certainly impacted the administration's judgment. For this mission, only boots on the ground could positively identify bin Laden, minimize collateral damage in a heavily populated area, and bring him (or his body) back, thus justifying this deep incursion into Pakistani territory. 

Success This Time Does Not Spell The End of Drones and Bombing

But just because a raid was used effectively this time does not mean that in all future operations the U.S. must first try the SEAL Team Six (DEVGRU) option. It also does not mean that the raid was required by human rights law, or that all future operations should be conducted pursuant to law enforcement rules. Rather, it was simply the best option among many military strategies. This time, the mission was reportedly accomplished with no civilian or military casualties. If, in the coming months, al-Qaeda figure Ayman al-Zawahiri or radical cleric Anwar al-Alwaki are found and can be targeted from the air rather than risking a human operation, nothing about the manner of bin Laden's demise should alter the decision to bomb either of them. 

Bin Laden was long thought to be hiding in a cave somewhere in Pakistan's Federally Administered Tribal Areas (FATA). As it turns out, he was in a mansion in an affluent neighborhood in Abbottabad. Had he chosen to hide in a cave, a missile or a bomb would have been a perfectly appropriate means by which to kill him. Of course, that's likely why bin Laden chose Abbottabad -- he knew that U.S. concerns over collateral damage were his best defense. What he didn't count on was that various detainees and intelligence assets would provide clues to those around him, that President Obama would be willing to authorize a raid rather than a bombing mission, and that the U.S. military would be able to carry out such an operation. Sunday's success did not prove that bombing and drones are no longer valuable as counterterrorism tools.  Rather, it taught us that they are one of many options available to the military when engaging terrorists.

Gregory S. McNeal is an associate professor of law at Pepperdine University, and blogs at LawandTerrorism.com