When hundreds of Nigerian school girls were kidnapped last month, perhaps one of the most horrific aspects of a thoroughly distressing crime was the overt threat by the Boko Haram members that they would sell the girls off into forced marriages.

For nearly five years, clashes between Boko Haram and Nigerian security forces have left many of Nigeria’s citizens living in a constant state of fear. But it wasn’t until this recent kidnapping that the insurgent group truly sprung to center stage.

Now that the Nigerian government claims that the girls have been located, doubt is growing over its ability to successfully extricate them from the clutches of the terrorist group alive, and concerns remain about the fate of the girls. The government has already stated that a military rescue would endanger the lives of the girls, and that a prisoner swap—the girls for imprisoned Boko Haram members—is out of the question. So the question becomes: If Boko Haram makes good on its threat to sell the girls into forced marriage, will it face any consequences for its actions?

That question has no easy answer. Rewire has learned that prosecuting members of Boko Haram for committing the “crime” of forced marriage could be a lot harder than we might have imagined. Our review of current laws shows a surprising reality: In 2014, there is still no written international law that explicitly makes forced marriage a crime.

How can this be? We know, for instance, that forced marriage, both of girls and women, as well as of boys and men, has played a part in numerous conflicts, including relatively recent wars—both civil and international.

From the systematic rape of women and girls in the Balkan conflicts and the Rwanda genocide, to the “bush wife” phenomenon during the Sierra Leone conflict, to the mass weddings under the Khmer Rouge regime, kidnapping, sexual slavery, and forced marriage are horrors that far too many women and girls face when the places they call home erupt into sectarian violence.

But despite the progress in international treaties and courts to recognize the gravity of sexual violence, when it comes to forced marriage in particular, there’s still no consensus on how to treat it as a matter of international law.

It’s a reality that many experts say leaves victims without adequate recognition of the very specific emotional, physical, and cultural trauma that forced marriage entails.

In an interview with Rewire, Amrita Kapur, a senior associate with the Gender Justice Program of the International Center for Transitional Justice, points out that forced marriage involves unique psychological harm not present in sexual slavery. That is due in part to the cultural implications of marriage in certain cultures.

“The connection with the community or the victims’ place in their own society is severed because in these cultures, when you do marry, you join your husband’s community,” says Kapur.

“You can certainly suffer stigma as a result of being a sexual slave,” she says. “But the return to the community doesn’t have the same type of connotation by being associated with the enemy.”

Kapur calls it a “double social harm.”

“The victim is forever identified as the wife of the enemy soldier,” she says.

Since at least 1948—in the Universal Declaration of Human Rights—marriage without consent of both parties has been recognized as a violation of international human rights law.

Nevertheless, forced marriage was not recognized as an international crime until 2008, when the Special Court of Sierra Leone (SCSL) issued its ruling against members of the Armed Forces Revolutionary Council, a rebel group which had perpetrated mass rape, forced marriage, and sexual slavery against women in that country. In that case, the court said forced marriage was a crime independent of sexual slavery, and held that forced marriage formed a distinct inhumane act of sufficient gravity to be considered a crime against humanity.

“[F]orced marriage involves a perpetrator compelling a person by force or threat of force, through the words or conduct of the perpetrator or those associated with him, into a forced conjugal association with another person resulting in great suffering, or serious physical or mental injury on the part of the victim,” the court said.

It was the first judgment of its kind.

The Sierra Leone tribunal also said there was a distinction between forced marriage and sexual slavery: Forced marriage, the court said, carries with it an element of relationship exclusivity not present in sexual slavery, as well as certain “benefits,” including, horrifically, protection from rape by other men.

The court also pointed out that forced marriage implied much more than rape, but a whole array of other, often forcible, duties, such as cleaning, cooking, child-rearing, and pregnancy.

These distinctions led the court to conclude that forced marriage is not predominantly a sexual crime.

It seemed as though this decision heralded a new determination to recognize forced marriage in international criminal law as a separate crime against humanity, but in fact, since then, those efforts have mostly stalled.

One reason is the lack of consensus in the international community as to how to address the crime.

Some scholars believe that forced marriage should be charged as a separate crime, and all physical and sexual violence suffered should form part of the offense of “forced marriage.”

Other experts balk at the Sierra Leone tribunal’s approach, raising the particular concern that the decision could reinforce patriarchal notions of what marriage is and incorporate gender stereotypes about women’s work—cooking, cleaning, and child-rearing—into international law. There is also a concern that charging forced marriage as a separate crime against humanity minimizes the sexual violence and enslavement that is the hallmark of forced marriage.

Kapur advocates for a more nuanced approach that considers the unique harms suffered under forced marriage. “I think the more nuanced approach would acknowledge that for forced marriage to be a distinct crime, the unique elements have to be sufficiently distinct to justify creating a new category.”

“The way you would argue that’s the case with forced marriage is that the unique element is the forced conjugal association and what the perversion of the institution of marriage does to the victims who are expected to perform ‘wifely’ duties,” she said.

“In Sierra Leone,” Kapur said, “a number of those victims were very explicit in saying that the type of harm that they suffered was not the same as being a sexual slave.”

Kapur recognizes that there is a lot of overlap between the two: “Sexual slavery and forced marriage often both have elements of forced labor, both have elements of sexual violence, and people have noted that forced marriage very rarely occurs without the sexual slavery and the sexual violence.”

“The real question,” she said, “is whether you say it’s worth recognizing that even though forced marriage has those elements, there’s something else there that needs to be recognized—that the type of harm is sufficiently different than that which would be experienced as a sexual slave.”

“It is quite possible in numerous cultures that the type of psychological harm that comes from the forced conjugal association is unique and should be recognized as such.”

The body most likely to prosecute a crime such as the forced marriage of the Nigerian school girls would be the International Criminal Court (ICC), which is empowered to investigate and prosecute crimes in four main areas: war crimes, crimes against humanity, genocide, and “aggression”—legalese for “war.”

The ICC’s authority is derived from the Rome Statute, which recognizes certain gender-based violence as crimes against humanity: rape, sexual slavery, enforced prostitution, forced pregnancy, and enforced sterilization. Forced marriage, however, is not among those crimes.

Importantly, the ICC is a court of last resort. It will step in and assume responsibility for prosecuting people accused of the most serious crimes of concern to the international community in situations where a nation is either unwilling or unable to do so itself.

Such is the case in Nigeria, which has been unsuccessfully battling the Boko Haram insurgency for nearly five years.

The ICC has already begun an investigation into Boko Haram. Last August, in a damning report, the ICC prosecutor said there is a reasonable basis to believe that the terrorist organization has been committing crimes against humanity—murder and persecution.

After an “investigation” that lasted more than two years, the ICC prosecutor found that Boko Haram had launched widespread attacks directed at the civilian population in different parts of Nigeria, including Borno, where the burned-out remains of the Chibok boarding school are located. The report estimates that more than 1,200 civilians have been killed in hundreds of suspected attacks against churches, banks, schools, and government buildings. The report also notes that these attacks have been committed pursuant to an organizational policy defined by the group’s leaders to establish an Islamic system of government in Nigeria.

And yet, despite the group’s longstanding history of sexual crimes, the report only mentions a single allegation of rape—and not a rape allegedly committed by a member of Boko Haram.

While not specifically enumerated as a crime against humanity, thanks to the Sierre Leone court judgment, there are now grounds to argue that forced marriage is an international crime that could be prosecuted in the ICC. The ICC prosecutor could hold Boko Haram accountable for selling the girls into marriage, by comparing the gravity of that crime to the crimes specifically listed in the Rome Statute—war crimes, crimes against humanity, genocide, or aggression—or charging it as an “other inhumane act” under Article 7(1)(k), the Rome Statute’s catch-all provision.

In either event, the ICC prosecutor would have to prove that forced marriage specifically was part of a widespread or systematic attack committed against a civilian population pursuant to organizational policy defined by Boko Haram’s leaders. And in order to hold the leaders directly responsible even if they did not actually kidnap the girls themselves, the ICC prosecutor would have to prove that they knew about it.

Certainly, the kidnapping of 276 Nigerian school girls seems like a widespread attack against a civilian population. But the prosecutor would have to consider how many girls, if any, were forced into marriage before bringing charges. (And now that the Nigerian government claims to have located the girls, it is unclear whether Abukubar Sekau, Boko Haram’s leader, has sold or will sell any of the school girls into marriage.)

In addition, it might be difficult for the ICC prosecutor to prove that forced marriage is an organizational policy. Sekau’s gleeful claims that he intends to marry off the girls could help satisfy that requirement. Generally, however, the ubiquity of violence against women during conflicts such as that raging in Nigeria has made it difficult to prove that the sexual attacks are part of a specific plan.

“Sexual violence is so tolerated and is committed with such impunity, that, paradoxically, it’s difficult to show that it’s part of a plan,” said Kapur.

While the crime of forced marriage has gone relatively unaddressed, the Sierra Leone court decision and the ongoing prosecution of Khmer Rouge leaders for crimes against humanity in Cambodia provide some guidance. Ultimately, however, this is a complex and developing area of international law with no simple solution.

Clarification: This story has been clarified to reflect the fact that, while the ubiquity of sexual crimes in the context of conflict often makes them difficult to prosecute as crimes against humanity, in the case of Boko Haram, the public comments from the group’s leader about his plans to sell the girls into forced marriage could make such a prosecution more attainable.