As reports poured in over the weekend that the United States bombed a Médecins Sans Frontières (MSF) hospital in Kunduz, Afghanistan, killing at least 12 MSF staff members and 10 patients and injuring 37 more, numerous commentators said that the strike was or could be a war crime or grave violation of international humanitarian law (IHL) (the laws of war).

The bombings took place as part of a military operation to take back the captured city of Kunduz from the Taliban. Eyewitnesses described in detail the horror of the strike, and the courage of MSF staff. An MSF nurse said:

[T]here are no words for how terrible it was. In the Intensive Care Unit six patients were burning in their beds. We looked for some staff that were supposed to be in the operating theatre. It was awful. A patient there on the operating table, dead, in the middle of the destruction. … We did an urgent surgery for one of our doctors. Unfortunately he died there on the office table. We did our best, but it wasn’t enough.

His entire account is an important read, especially for those in the US who typically only see reports that an “airstrike was conducted,” but not the harrowing details of their impacts. The hospital was also the only trauma center in Kunduz, and the civilian population heavily relied upon it in a region under going heavy fighting.

In response to the attack, MSF officials called it “abhorrent and a grave violation of international humanitarian law,” and said that they presume a “war crime has been committed.” The United Nations’ human rights chief, Zeid Ra’ad al-Hussein said the event “is utterly tragic, inexcusable, and possibly even criminal,” and that “the seriousness of the incident is underlined by the fact that, if established as deliberate in a court of law, an airstrike on a hospital may amount to a war crime.” The International Committee of the Red Cross (ICRC) condemned the bombing and Human Rights Watch said that the airstrikes raise “grave concerns about whether US forces took sufficient precautions to identify and avoid striking the facility.”

Did the United States violate IHL in this attack, and did the individuals responsible commit a war crime?

The answer depends on numerous factors, at least some of which have not been publicly reported or which are at present contested, and the legal assessment requires consideration of various intricate rules.

Here I briefly set out four of the possible factual scenarios based on the reports and witness accounts to date, and (below) some of the key legal concerns, questions, and implications:

a. The US intentionally bombed what it knew to be a hospital that was used only for medical services.
b. The US intended to bomb Taliban fighters it believed were in the hospital building but the US did not know that it was bombing a hospital.
c. The US intended to bomb Taliban fighters located near the hospital, and unknowingly also hit the hospital.
d. The US intended to bomb Taliban fighters who it believed were located in, or near, what the US knew to be a hospital.

International law provides general protections for civilians, and special protections for hospitals and medical professionals which cannot be the object of an attack as such. These protections remain even if the enemy is receiving treatment inside the hospital. Hospitals may, however, lose their protected status if they are being used by the enemy to launch attacks. If this happens, IHL can permit certain attacks on such hospitals, but still requires, for example, forces to take precaution in attacks to minimize or avoid harm to civilians and protected objects, including hospitals. Additionally, forces must ensure that an attack is not expected to cause civilian harm that is excessive to the anticipated military advantage (the proportionality rule).

If scenario (a) is assumed, and the United States intentionally bombed a hospital used only for civilian and medical purposes, then the United States would have likely violated IHL, and the individuals involved may have committed a war crime (e.g., Rome Statute, Article 8(2)(e)(iv)). This would hold true even if the hospital was treating Taliban war wounded. (Indeed, intentionally attacking wounded fighters can also be a war crime: Rome Statute, Article 8(2)(c)(i)). As of now, there’s no strong evidence to suggest that scenario (a) occurred.

If scenario (b) is assumed, and the Unites States intended to bomb Taliban fighters but did not know that it was also bombing a hospital, the legal analysis would hinge in large part on whether the United States took or failed to take the necessary precautions — before it began bombing — to protect civilians, medical personnel, and hospitals.

Those who plan and decide attacks are required to “do everything feasible to verify that the objectives to be attacked are neither civilian nor civilian objects and are not subject to special protections.” The planners must also take all feasible measure to choose the means and methods of attack with the view of avoiding, or at least minimizing, incidental loss of civilian life and injury to civilians and civilian objects.

The US and Afghan armed forces reasonably could and should have known information such as where the MSF hospital was located and whether it was still in use. MSF reported that it gave US and Afghan forces the coordinates of the hospital as recently as September 29. Media outlets have reported (see here and here) that the strike was called in by ground forces coming under Taliban fire, but while such a fact (if true) would shorten the time available for precautionary steps to be taken, it was not the first time the United States had the opportunity to acquire information about the hospital. It was, at least, last Wednesday when US advisors and airstrikes began to assist Afghan special forces to retake Kunduz from the Taliban. If, by Saturday, the US military did not know information about the MSF hospital, there is very good reason to ask why not.

In addition to the responsibilities that planners of an attack have, those carrying out an attack must also cancel or suspend the attack “if it becomes apparent that the objective is not a military one or is subject to special protection.” The ICRC explains that this could come about through visual observations of, say, a pilot. Here it would be important to ask, for example, if a red cross or other telling emblem were painted on the roof of the MSF hospital or displayed elsewhere, was the pilot able to see that emblem? If the pilot did, how did they respond? Did they ask for a confirmation to strike? If so, was it approved and under whose orders and under what considerations? And, why did the bombings continue for a reported half an hour after MSF reported to US forces that they had been hit? The precautionary rules would also have applied to the ground forces — whether US or Afghan — who called in the strike if they became aware that the bombing target was a hospital.

If scenario (c) is assumed, and the United States intended to bomb Taliban fighters near the hospital, but did not know a hospital was nearby, many of the same issues as in scenario (b) would be relevant to determining legal liability. Key questions would be: Why didn’t the United States know that there was a hospital in the area of attack? What other precautionary steps did the US take or not take before the attack?

If scenario (d) is assumed, and the United States intended to bomb Taliban fighters while knowing that they were located in, or around, a hospital, one of the most important legal questions would become: What kind of proportionality assessment was made and what steps were taken to minimize civilian harm? Did the United States know when it carried out the strike that, amongst other grave consequences, nearly two dozen civilians would be killed and many others injured?

As a factual matter, MSF adamantly disputes allegations that the Taliban were attacking from the hospital. But, even if they were — and such Taliban actions would be unlawful under the laws of war — this does not permit carte blanche bombing. The strike must still meet the requirements of proportionality and feasible precautions taken in attack.

Some reports have suggested that Taliban fighters were in the proximity of the hospital, which presumably means that the hospital and the people inside could have been killed and injured as a result of debris from nearby bombings. MSF refuted that account as well, but if it were true, it would also raise concerns about whether proper precautions in attack were taken.

If the United States knew the location and nature of the hospital, and bombed it, or the area around it, because Taliban attacks were coming from the hospital or the surrounding vicinity, IHL would require the attack to be proportionate: those who plan and decide an attack must refrain from launching any attack “which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.” If the expected civilian harm is not excessive to the anticipated advantage, then the attack can go forward. (I emphasize these words to highlight the elements of the rule that create latitude in targeting and insulate forces from liability). The proportionality rule falls not only on those planning and deciding the attack, but also on those carrying out the attack, who have the obligation to cancel or suspend the attack if it becomes apparent that it will not be proportionate.

Important facts that we do not know include, for example, the exact target of the US strikes, the intent and pace of the operation, how significant this attack was in the effort to take back Kunduz, or what the pilots knew at the time of the attack. Nonetheless, it is clear that the civilian harm was extremely significant, and the US would need to explain either how such significant devastation to civilian life and property was justified by “military advantage” or what it believed the consequences would be at the time of the attack.

Given the complexity of the facts and law, the seriousness of the harm, and the gravity of the alleged legal violations, it is critical that the United States conduct a thorough and independent investigation, and, that it explain to MSF, its patients and their families, and the international community how this attack happened, whether anyone is held accountable, and what lessons were learned. The United States, which has committed to undertake an investigation, need only take the good advice it gave last week to those responsible for civilian harm in Yemen:

We … have underscored the importance of thoroughly investigating all credible allegations of civilian casualties. We call for an investigations into these reported civilian casualties and for the findings to be reported publicly.