Sister Diana Muñoz Alba didn’t have to reach back very far to illustrate the horrors that migrants face deep in Mexico’s impoverished Chiapas region. Speaking to an audience gathered Wednesday at the Church of the United Nations—the UN headquarters and the member countries’ flags were framed in the windows behind her—she recalled what happened on April 19.

Sergio, a nineteen-year-old Guatemalan, died that day as a result of extreme dehydration suffered on the long, hot walk to cross Mexico’s southern border. Sergio and four cousins had each paid a smuggler $3,000 to bring them across the border—without food or water. When they arrived at the Santa Martha Migrants’ Shelter in Salto de Agua, Sergio was sick, so sick that the smuggler left at daybreak, warning him not to talk. By the afternoon, he was convulsing and feverish. A doctor managed to control his fever and convulsions, and then Sister Diana, the shelter’s director, went with him on the ninety-minute ambulance ride to the hospital. But within three hours, Sergio died after suffering a stroke that caused seizures.

Sister Diana, who spoke in Spanish beside a translator, was quiet and matter-of-fact: “we only have a bedroom for men with a capacity for forty people sleeping on mats, a bedroom for women with capacity for twenty-five people, a kitchen, a space for registration, and a small space for nursing and clothing,” she said. Last month, she helped 1,180 people, and 1,105 the month before. At the shelter, she said, “we lack everything: food, medicine, clothing, shoes, beds, fans.”

But quiet as she was, she was a voice from the periphery who challenged the United Nations, religious leaders, and the U.S. and Mexican governments—really, all of us—to do more to prevent the kind of suffering she sees as a matter of routine, as thousands of migrants surge north from Central America into Mexico. The people arriving at Santa Martha shelter “have usually been the victims of countless violations of their rights, such as assaults, kidnappings, sexual violations, extortion, and violent operations carried out in collaboration with the national army, the navy, and the state and municipal police,” she said.

Sister Diana, an immigration lawyer, was part of a panel discussion connected to an effort by the Holy See Mission to the United Nations and Caritas to “bring forth a moral approach” to the UN’s planned Global Compact on Migration. (Franciscans International and the Scalabrini International Migration Network sponsored the event.) The Trump administration withdrew the United States from the process on December 3 on grounds that it “could undermine the sovereign right of the United States to enforce our immigration laws and secure our borders,” but 192 nations continue to work on the compact.

In the meantime, Sister Diana witnesses a steady flow of trauma: Aida, a twenty-four-year-old Honduran woman, died on April 12 after her legs were severed by a speeding train she tried to board. Or, “a few days ago we received an unaccompanied minor” whom a migration police officer had thrown off a train, causing serious head injuries and a mangled ear.

Sister Diana didn’t raise it herself, but her Franciscan example—she is a member of the Franciscan Missionaries of Mary—poses the question of why churches in the United States only rarely offer refuge to undocumented migrants.

The Reverend Julian Jagudilla, a Franciscan who is director of the Migrants’ Center at St. Francis of Assisi Church in Manhattan, picked up on this in his remarks. “Churches, especially Catholic churches, refuse to offer sanctuary to individuals facing deportation,” he said.

While some mainline Protestant churches have done so, few, if any, Catholic parishes in the United States are known to offer sanctuary to undocumented immigrants.

Sister Diana’s challenge to the Mexican government was direct. She urged that it stop “implementing the requests of the United States government” and “not turn a blind eye when they have full knowledge of…the people who are violating the migrants.”

From the periphery, Sister Diana sorts out, with a lawyer’s precision, a nexus of evil that sounds like a Graham Greene novel (and Greene did visit Salto de Agua). She spoke of smugglers who have threatened her or delivered migrants to organized crime. She said the authorities “often participate in the aggressions” and that she has heard “countless times” that they cooperated with kidnappings.

“The law in Mexico establishes the right to free transit,” she said. “However, the passage through Mexico for migrants becomes a Calvary in which many of them lose.”