It began, in one way at least, on a Saturday in early 2011, outside of a bodega called El Tal Iván in Iztapalapa, one of the poorest neighborhoods in Mexico City and a recent nexus for violent crime.

According to an account in the newspaper La Jornada, six young people had gathered there late at night when a passing car fired 25 9-mm. bullets at them. Five were killed immediately. The sole survivor, a pregnant woman in her early 20s, was rushed to a public hospital with a punctured lung. She was in danger of bleeding to death.

There have been at least 360,000 cartel-linked homicides in Mexico since the government declared war on the gangs in 2006, according to the Council on Foreign Relations. Many of the dead, and countless injured, pass through the nation’s hospitals, which the cartels specifically target for some of their cruelest acts of violence.

Dr. José Luis Mosso Vázquez, an emergency surgeon at the hospital, helped to stabilize the survivor of the drive-by shooting. Although he had seen many victims of cartel violence, this case stayed with him. He asked after the woman every few days as she lay nestled amid tubes and machines in the hospital. At first the news was tentatively good, for both mother and baby. Then one day the tone abruptly changed. The mother had died, the baby too. How was such a thing possible? he asked.

Mixing science and superstition: Dr. José Luis Mosso Vázquez.

He was told that the cartel responsible for the shooting had called the intensive-care unit and issued an ultimatum: if Dr. Vázquez’s patient was not disconnected from the machines keeping her alive, they would pay the hospital a visit and kill everyone on the ward. According to Dr. Vázquez’s account, which we have not been able to independently corroborate, the machines were switched off. Everyone has been too afraid to talk about it since, he says.

And that is why, several years later, when Dr. Vázquez embarked on an experiment to prove the existence of good and evil, of God and the Devil, he used the cartels as a point of comparison—the baseline for human fear.

I originally stumbled across the details of his work during the first pandemic lockdown. It was an academic paper, in a pay-to-publish medical journal, entitled “Experience of health professionals around an exorcism: A case report.”

It described how, in April 2017 in Mexico City, an exorcism was conducted under medical supervision using hospital scanners. It also described a strange aftermath to the experiment. Of the 13 people involved in the exorcism, 8 suffered accidents, illnesses, accusations of sexual harassment, and “unusual phenomena” in the 57 days around the experiment.

Dr. Vázquez embarked on an experiment to prove the existence of good and evil, of God and the Devil.

The paper asked the health personnel involved to rank their fear of “the devil” against their fear of “organized crime.” Eight of the participants said that while they believed in the Devil, cartel violence was of much greater concern. The paper’s implication was clear: these were unsuperstitious doctors and medical assistants, not prone to hysteria, who had been subjected to a very real curse.

When confronted with this experiment, the rational part of my mind told me that even if demons did exist, hospital scanners were no more likely to reveal them than a toaster. But it was 2020. Pandemic lockdown. Outside my own door, pestilence stalked the earth. Death was a daily conversation. Religion had resurfaced among even the secular in the form of tribal politics and theologically elaborate conspiracy theories. The blend of science, fear, superstition, the rational, and the messianic was everywhere. I felt compelled to find out more.

The Doctor’s Dilemma

Dr. Vázquez is an intense, dark-haired man. He is around 60 but appears much younger. As well as being an emergency surgeon, he was a research professor at the Catholic college Universidad Panamericana. He specialized in research on laparoscopic surgery, the use of remote tools and video to conduct minimally invasive operations. Dr. Vázquez was also responsible for performing the first robotic surgery, using computerized equipment, in Mexico.

Dr. Richard Satava, an emeritus professor of surgery at the University of Washington, and a former program manager with the Defense Advanced Research Projects Agency, more often known simply as Darpa, had served as a close adviser to Dr. Vásquez. He said Dr. Vázquez was a very clever developer of inexpensive surgical devices—including one that turned cell phones into surgery monitors—that were vital in the underfunded Mexican health-care system. Indeed, in 2017, Dr. Vázquez was featured in The Atlantic for using a rudimentary V.R. headset as a “high-tech distraction technique to carry out surgeries that would normally require powerful painkillers and sedatives,” another useful and cheap technique for underfunded Mexican doctors.

But Dr. Vázquez told me that alongside cutting-edge science he also follows more ancient traditions. “I am of indigenous origin,” he said. “My dad was indigenous, and all his family. They don’t speak Spanish; they live in the mountains of the state of Guerrero. They don’t come down to the civilization we know. And among their ancestral customs and traditions, they practice a series of spiritual rituals,” he said.

This is not unusual. Mexican spiritual life revolves around Catholicism but has an easy relationship with other, more occult religious practices. Examples of brujería—the Spanish word for witchcraft—abound in Mexico City. As do images and statues that refer to Santa Muerte, the goddess of death, or to Santería, a religion that combines Yoruba with Catholicism and spiritism.

An altar to Santa Muerte sits near the border between the United States and Mexico.

Dr. Vázquez says he follows shamanism. His aunt was a shaman who could leave her body and possess others. “She did it with me,” he says. “She did a series of things to me that, well, I think now is not the time to go into it. But she awakened in me the study of those areas that humans can’t explain yet.”

And so, in 2016, at the very height of Dr. Vázquez’s exposure to cartel violence, he decided to embark on the ultimate scientific foray into the inexplicable.

Through a priest named Father Cuitlahuac, he was put in contact with Maria (not her real name), a young woman whom the Catholic Church had certified as being demonically possessed. Dr Vázquez commissioned a psychological report on her. It described “a 29-year-old female patient, an only child from Mexico City, from a middle socio-economic background from a dysfunctional family with an alcoholic, intolerant and abusive father and a submissive mother with paternal lines of all intolerant aggressive uncles.”

In the report, Maria describes how, when she was a child, she saw “a ghost with the head of a bull and horns with the torso of an animal.” Later, she described becoming pregnant by a former boyfriend who had links to the occult, and having an abortion. At around this time, her father and his friends performed a ceremony to rid her of evil spirits in which she was placed inside a circle of fire.

The possession began when she was 20. “During the possessions,” she said, “my body begins to distort, the entity begins to speak. The entity is very cunning, it knows what is going to happen, it knows the future.” She says it has raped her and physically hurts her when she tries to pray. She is wracked by pain and vomits for no reason. A prescription for the powerful anti-anxiety medicine Klonopin helps only slightly.

Another section of the report details her parents’ observations of the exorcisms Maria has undergone through the years. They describe their daughter speaking “a strange and ancient language,” sticking out her tongue to an alarming degree, and moving around like an animal. Large black flies suddenly appeared, and the pupils of her eyes became vertical, like those of a cat or reptile. They say she became afraid of an image of Pope John Paul II.

Maria blames herself. She believes the possession is punishment for her abortion, for having multiple sexual partners, for giving up college. “I believe that demons come from one’s sins or from one’s ancestors,” she says.

She had previously undergone five exorcisms, each taking eight hours, conducted according to the strict rites of the Catholic Church. It is hard to say how common exorcisms are in Mexico, as no statistics are kept, but news reports suggest a growing number in recent years. The Catholic Church exorcised the entire nation in a ceremony on May 20, 2015, out of a fear the country was being overcome by cartel violence and other evils.

“I believe that demons come from one’s sins or from one’s ancestors.”

Dr. Vásquez’s plan was simple. He wanted to see inside Maria’s brain during an exorcism. He wanted to watch the demon battle the priest for her soul, and finally, to witness the cleansing light of the Holy Spirit entering her body, banishing the evil forever.

To do this, he had secured the use of a General Electric 3.0 Tesla Magnetic Resonance Imaging (M.R.I.) scanner. An M.R.I. scanner, when used as part of a specialized technique known as fM.R.I., allows scientists to “see” the brain work. The machines are often used in the field of neuroscience to study the human nervous system, from its basic physical functions to the deepest and most nuanced secrets of memory, behavior, perception, and even consciousness.

The images and video of the experiment that I have seen show Maria, wearing hospital slippers, patterned athleisure pants, and a blue hospital gown, lying on the extended gurney of the room-size machine, being connected to monitors by snaking cables, clips, and pads.

In an adjoining room, behind a one-way mirror and a tinny communication system, Dr. Vásquez watched the screens that would display Maria’s brain and vital metrics. As the gurney whirred backwards, drawing Maria into the M.R.I. tube, the exorcist appeared. It was Father Cuitlahuac himself, a bearded, bespectacled man in his 50s who emerged into the room in full ceremonial garb, a purple sash around his neck, wielding a Bible like a shield. He began to demand that the demons depart Maria forever.

Maria lay perfectly still. In fact, compared with her previous exorcisms, the demons seemed quite unperturbed. There were no strange languages heard nor animal movements seen, but when she eventually emerged from the M.R.I. tube, she vomited “a foul and voluminous concoction,” according to Dr. Vázquez. The brain scans, while showing some changes, were inconclusive.

When I asked Dr. Satava, who had helped Dr. Vázquez on previous experiments, to interpret these findings, he said: “We don’t have any neuroscientific measurable metrics or baselines on evil or good or on a soul. So it is not possible at this time to validate them. The soul must remain in the cradle of faith and personal beliefs rather than scientific fact.”

A memorial to murdered women on the outskirts of the border town of Ciudad Juárez.

Dr. Vázquez agrees that neuroscience is limited. But he feels that is in part because it declines to address the spiritual parts of humanity. “We still need to know ourselves better,” he said. Just as important to him was that, following the experiment, many of the participants reported strange misfortunes.

Maria began experiencing strange losses of consciousness, alongside the vomiting. Her father suffered a heart attack. Dr. Vázquez himself was hiking when, after stopping to rest, he found a small brown snake in his pants—something he considered a very bad portent. Shortly afterward he fell and severely injured himself. In the aftermath of the accident he was unexpectedly brought to the exact same M.R.I. scanner used in the exorcism.

Father Cuitlahuac alleged that he was sexually harassed by two women in his church. A gynecologist present was accused, by her brother, of a crime she did not commit. Another doctor involved in the experiment decided suddenly to break up with her boyfriend of 10 years. A neuropsychologist, in charge of monitoring the M.R.I., disappeared for 49 days and has still not explained where she went.

“The soul must remain in the cradle of faith and personal beliefs rather than scientific fact.”

As I wrote about Dr. Vázquez’s experiment from a safe distance, this “curse” seemed like nothing more than workaday misfortunes that hardly required demons to explain them. My editors began to wonder if the experiment had been a hoax, an attempt to garner attention by publishing a dubious study in a pay-to-play medical journal. But Dr. Vázquez had seemed so heartfelt, and everything he told me about himself had checked out. My own protective rationality—the reassuring idea that every problem can be defined and explained into safe certainties—was wavering.

I could not get the word “curse” out of my mind. I joked about it. But when anything untoward happened to me while I worked on this story—when I got norovirus, when I bruised my ankle on the leg of my sofa, when my debit card went missing—the word “demon” flashed through my mind. I consulted a Mexican medium who told me to wear a red ribbon around my waist to ward off evil whenever I worked on the story, and not to download materials connected with the experiment.

I wanted to understand more, so, in collaboration with Mariana Roa Oliva, a researcher and reporter in Mexico City, and with Dr. Vázquez’s help, I tried to contact the participants in the experiment to ask for their recollections and impressions.

The Devil’s Disciple

We could reach Maria only via her father. He said she did not want to speak to us. When we asked to talk to him, he provided a phone number that did not work. Carlos Jesús Castañeda Gonzalez, the paper’s co-author, set a time for an interview but then said he was busy and would call us back. He never did, and did not answer his phone when we tried to call him. Every other participant in the experiment declined to talk to us or provide any details. Some set appointments but then missed them and sent us improbable excuses to explain their absence. It seemed like they were scared.

Only Dr. Virginia Ramírez Nova, a consultant on the experiment, agreed to talk. “When the article came out, he sent it to me [to consult on], and I was rather neutral,” she said. She had taken an academic interest in the paper and was reading it at home one night when the lights in her apartment began flashing on and off. She said the computer she was reading it on immediately went blank, and she has not been able to revive it since.

She has never read the full article, and never will. She regretted agreeing to talk about it again. “Most of us physicians have very rigid minds; we don’t talk about these things,” she says. “Even myself, I might say this doesn’t exist, but now that I’ve lived it … ” She trailed off.

The last person we tried to find was Father Cuitlahuac, the priest who had intoned the Word of God into a mechanical tube. We discovered he worked at Rectoría del Espíritu Santo, an old yellow church with an open bell tower overlooking its steps in the east of Mexico City.

To get there, one can walk through Mercado de Sonora, a large market that started decades ago in the narrow, winding streets to the southeast of the city. It is renowned for examples of





and for rows of statues, shrines, and objects devoted to Santa Muerte and Santeria. Skulls, skeletons, and grotesquely disfigured dolls are piled in stalls not far from beatific images of the baby Jesus, and boxes of puppies and cages of birds packed so tightly they can’t move.

It was Domingo de Ramos, the start of Holy Week, seven days before Easter Sunday. The church had just closed, but devotees were still selling palm decorations outside. Mariana asked two of the older women if they knew the priest. They looked at each other in surprise. Father Cuitlahuac had died suddenly a little while back, they said. It was right after morning mass. He had just taken off his robes. They didn’t know the exact cause.

Ravi Somaiya is a New York–based writer and editor. His book The Golden Thread, about the mysterious death of Dag Hammarskjöld, is available now