“We cannot return to Rwanda,” the young man in the sweat-stained Denver Broncos T-shirt told me earnestly. “We are Hutus, you see, and were we to do so we would surely be killed.”

It was a hot day in the early fall of 1994, and we were standing on the grounds of the cathedral in the center of Goma in what was then eastern Zaire. So great was the crush of people that it was hard to hear everything he was saying. And his friends constantly interrupted him. “We can’t be sent back,” one of them declared. “That would be immoral. We would be killed.” “Not just immoral,” a third young man added, “it would be illegal. A UNHCR [United Nations High Commissioner for Refugees] official told us that only this morning. We cannot be sent back. That would be refoulement.”

There was a hush after the word was uttered. It was this prohibition against refoulement, which means the forced return of a person to a country where he or she faces persecution, that provided for these destitute Hutus their only possible protection against being killed. Defeated on the battlefield, decimated by the cholera epidemic that had exacted a fierce toll from them when they had first arrived from Rwanda, they had discovered the saving grace of refugee law, and repeated its provisions like a mantra.

“We are refugees. We cannot be made to go back home,” the young man said, “Would you be willing to return to Rwanda if you were in our place?”

The answer to that was easy enough, but the reasons were far more complicated than the refugees wanted to admit. Of the more than 2 million people who fled Rwanda in the aftermath of the genocide of the spring and early summer of 1994 in which between 500,000 and 1 million Tutsis and liberal Hutus were killed, tens of thousands (at a conservative estimate) were either soldiers and officials of the defeated Hutu regime. Many thousands more had been caught up in the frenzy of killing and were guilty of murdering their Tutsi neighbors. But hundreds of thousands of others had played no role in the genocide including thousands of children, many born in the UNHCR-administered refugee camps.

Separating those who were not entitled to refugee status from those who were was an impossible task for UNHCR officials, whose experience lay more in trying to secure the protections refugees are entitled to under international law than in separating legitimate refugees from soldiers who had crossed the border, or from criminals who had committed crimes in Rwanda and whose return there would have been an act of justice, not a violation of international law. The United Nations Convention Relating to the Status of Refugees and its 1967 Additional Protocol stipulated that refugees could not be returned to a place where they faced persecution. But surely its architects had never imagined a situation like the one that occurred in Goma.

Previously, most instances of refoulement involved individuals fleeing across an international border, or, in some cases, moving on to a third country, and claiming that, were they sent home, they would face persecution. An Iraqi Kurd arriving at the Frankfurt airport and being sent home, a Haitian making her way to Miami in a leaky boat and being towed back to Port-au-Prince by a U.S. Coast Guard cutter—these are the instances of refoulement over which international law has some intellectual and moral purchase. In this context, it is possible to talk about the requirements for what constitutes “persecution” within the meaning of the refugee convention; in practice, these requirements differ in interpretation from country to country, but in principle any person who can legitimately claim refugee status is protected from refoulement. Only when a person ceases to be a refugee does the rule against refoulement cease to apply. The real debate is when a refugee gets the right. Are illegal aliens covered? Some countries believe they are; others do not. Does a person have to enter a country officially to get refugee status and the accompanying protection against refoulement? Again, the opinions of international lawyers and governments differ.

What became clear in Goma was that in instances of mass migration—where children and murderers arrive in a great mass, and separating them is neither easy nor safe—the law is very hard to use, and harder still to use appropriately. Nobody in those camps wanted to return to Rwanda; many had killed before, and there was no reason to suppose they would not kill again.

For UNHCR, it was better to err on the side of maintaining its protection mandate and the prohibition against refoulement than to send back people who feared persecution in a Rwanda where power had changed hands; even if doing so meant, in practical terms, allowing mass murderers to claim the rights of innocent refugees. For those who wanted the Rwandan crisis to be brought to a close, and saw in the refugee camps little more than a safe haven for those who had perpetrated the genocide and their dependents, the prohibition against refoulement seemed like madness.

For two years, UNHCR’s view prevailed. Then, the Rwandan Army struck at the camps. Most refugees were forced back across the border. It was an unhappy solution to a problem for which legal definitions of refugee status and legal prohibitions against refoulement only serve as poor guides.