I was in Germany when Osama bin Laden was killed in a U.S. military operation in Abbottabad, Pakistan on May 2. German news coverage of the killing repeatedly raised one question about the incident: Did the attack violate international law? An interviewer on ZDF television asked this of former U.S. ambassador to Germany, John Kornblum, who responded that he was sure it was lawful. But that was all he said - he did not explain why.

The Ambassador is probably correct, but it is a closer case than he may realize. The question turns on one critical factor: President Obama's orders to the Navy SEAL team that carried out the raid on bin Laden's compound in Abbottabad.

Orders to kill, not capture, bin Laden would be difficult to defend legally. But top counterterrorism adviser John Brennan stated Monday that the SEALs were under orders to capture bin Laden if they could. CIA chief Leon Panetta has implied, on the other hand, that the team was under orders to kill, with the option to capture if he attempted to surrender. If Panetta is correct, the legal case is weakened but can still be defended.

The use of lethal force is governed by two types of international law: the law of peace and the law of armed conflict. In peace, international law supports national legal systems when it comes to the resort to force. National systems restrict the use of force to law enforcement authorities -- the police, or in special circumstances, the military (I argue here that the SEALs, who are military, kept their use of force at law enforcement levels). Unauthorized persons may resort to force in self-defense if necessary to save a life immediately. Otherwise, using force is considered a crime under international law.

Some crimes are so serious they are outlawed in international law, as well as national law, with the crime of terrorism as a prime example. As an international crime, states around the world have an obligation to suppress terrorism. But in suppressing even the most serious crimes, law enforcement agents must limit the amount of lethal force they use, and excessive force, even in anti-terrorism cases, has been ruled a violation of human rights law by both the European Court of Human Rights [ECHR] and the Inter-American Court.

The ECHR considered a case in 1995 with parallels to the bin Laden raid. In McCann v. The United Kingdom, the court found that members of the elite British SAS used excessive force when they killed IRA members in Gibraltar who were suspected of preparing a bombing. The court found that the operatives should have attempted to arrest the terrorists, instead of shooting them based on intelligence they possessed that the suspects were preparing to use explosives. If the suspects had resisted arrest or attempted to escape, authorities then would have had had the right to resort to lethal force.

This is the law that applied in bin Laden's case. On May 2, no fighting was going on in Pakistan that would rise to the level of "armed conflict" as defined under international law; Pakistan had to suspend major military operations against militant groups in the country's tribal areas after the floods of 2010. And despite what some commentators have argued, under international law there is no right to engage in cross-border military force based on the argument that a state is unable or unwilling to deal with the threat themselves. The correct choice of law, therefore, was peacetime law.

The U.S. government has said that the SEALs killed bin Laden while he was resisting. He was apparently unarmed, though CIA director Panetta has said he made "threatening moves." The SEAL team had had to fight their way into the room; they were in an extremely dangerous situation. They had to consider whether bin Laden had weapons available, full in the knowledge that bin Laden was highly dangerous and that it was imperative that he not escape. As the respected U.N. Special Rapporteur on human rights Martin Scheinin has commented, authorities must be prepared to use force in capturing dangerous criminals, while noting that surrender was a choice, and that, "Bin Laden would have avoided destruction if he had raised a white flag."

One important difference from the McCann case, of course, is that the SAS carried out their action on British Crown territory. Media reports indicate that the U.S. kept the bin Laden operation secret from Pakistan until the moment the raid was launched. In ordinary circumstances, states must refrain from carrying out law enforcement action on another state's territory without that state's permission.  However, in this case the Pakistani leaders initially expressed satisfaction with the action, thus waiving claims of a violation. They have also expressed the strong position that the bin Laden operation not become a precedent. This is a statement the Pakistani government needed to make to reestablish their rights under international law to territorial integrity.  The U.S. should expect no similar waivers in the future.   

Even if Pakistani leaders did not waive their rights, the U.S. raid in Abbottabad can arguably be justified under the law of countermeasures. Countermeasures are otherwise unlawful actions taken in response to a prior unlawful action, if necessary and proportional to respond to the initial wrong. Economic sanctions, for example, are a common form of countermeasure. Pakistan has failed for years to comply with international obligations to suppress terrorism, especially those requiring it to search diligently for bin Laden and to prosecute or extradite him. For this, the countermeasure of violating Pakistani territory to carry out a police action was, arguably, necessary and proportional.

What cannot be justified as a countermeasure is the use of military force. The resort to military force on another state's territory is governed by the U.N. Charter which restricts the resort to force to a few exceptional situations: military force may only be used on the territory of a state if that state has attacked first; if the U.N. Security Council has given authorization (as in the case of Libya), or if there is an invitation by the host country to suppress an insurrection (as in Afghanistan). None of these exceptions apply to Pakistan, so while the bin Laden killing may have been "acquiesced in" (to use the legal term of art) after the fact, the targeted killing of so many others in Pakistan by the U.S. is not.

Since 2004, the U.S. has conducted targeted killing in Pakistan with the use of drones carrying Hellfire or other missiles. In other words, unlike the law enforcement action carried out against bin Laden, the U.S. uses military force against other terrorist suspects in Pakistan.  These operations could be justified if they were carried by U.S. military personnel -- not the CIA -- and if they occurred during Pakistani military operations, at Pakistan's request. But U.S. drone strikes in Pakistan have not met these legal requirements.  These operations make no known attempts to capture the militants targeted in the strikes, only to kill. The U.S. kills not only the suspect but also often others around them-even though in international law there is no justification for collateral deaths outside of armed conflict.

The U.S. may, in fact, have afforded bin Laden and the people around him more rights than it has to others about whom the U.S. knows little -- that is, if Obama's order was to capture or kill, rather than just kill, bin Laden. Even if the order was to kill, the use of assault rifles, rather than missiles and bombs, meant some 20 people in the compound survived the operation.

Both the Bush and Obama administrations have tried to justify killings in Pakistan by arguing that the U.S. is in a "global war on terror" or in an "armed conflict against al Qaeda, the Taliban and associated forces." The international community does not accept these claims and persisting with them may ultimately cause the U.S. more harm than good. (See for instance Scheinin's opposition to the "war on terror" also referred to in the link above and the Final Report on the Meaning of Armed Conflict in International Law.)

With the death of bin Laden, it is also time to end the "war" on terror-and return to police measures that sometimes involve the use of force.  It would be a dark irony if the methods that worked against Bin Laden were rejected for his lesser lieutenants.

Mary Ellen O'Connell is the Robert and Marion Short Chair in Law and Research Professor of International Dispute Resolution at the Kroc Institute at the University of Notre Dame, as well as the Vice President of the American Society of International Law.