After Sylvia Saucedo and her mother survived the shooting in El Paso, Saucedo was swarmed and attacked for bearing witness. Photograph Courtesy Sylvia Saucedo

Last Saturday morning, Sylvia Saucedo had her dog Sasha, who was old and ill, put to sleep. The dog “was like a member of our family,” Saucedo told me recently, sitting in her darkened den, in El Paso, surrounded by family pictures: a bullfighting brother who’d died from a heart attack; a Vietnam-veteran brother who’d died of cancer; her father, born in Juárez, who’d died, at eighty-two, after suffering multiple strokes. A fifty-eight-year-old former military-base accountant—who suffers from rheumatoid arthritis, pulmonary fibrosis, and fibromyalgia, which forced her to retire early—Saucedo is active and upbeat on Facebook. She frequently posts pictures of her ninety-one-year-old mother, Silvestra; religious musings; favorite expressions in English and Spanish; and lots of emojis. At a quarter to six, on the same morning she said goodbye to her dog, she’d shared a quote attributed to Jane Goodall: “How is it possible that the most intellectual creature to ever walk the planet Earth is destroying its only home?” A few hours later, at 7:26 A.M., she took a photo of Silvestra lying down exhausted in bed in the house that they share. It had been a long week of mourning.

As a distraction from losing Sasha, and because they needed groceries, Sylvia and Silvestra drove to the Walmart four miles away, at the Cielo Vista Mall. While she was parking, Sylvia received a text from a friend inviting her to breakfast. She sent back a picture of the Walmart lot, at 9:21 A.M. Inside, they shopped. Then, smelling pancakes wafting from the McDonald’s within the store, they decided to have breakfast. “Thank God we stayed there,” Sylvia told me.

Midway through their meal, as her mother sipped her coffee, Sylvia noticed people running inside the store. “It must be a big sale,” her mother quipped. Sylvia sensed that something was wrong. “That’s when we heard the shots from the parking lot, by the main door,” Sylvia told me, which was only twenty feet away. “The cashier lady said, ‘¡Tirense en el suelo, esto es un tiroteo!’ ” (“Get on the floor, this is a shooting!”) “Mom got stuck on the bench, so I pulled her down by her blouse. She fell. I was afraid she’d break something.” Sylvia called 911. No answer. She called again, with the same result. “So I started recording with one hand,” she said. With the other, she held her mother, who was quietly praying and crying. “Her cheeks were shaking with every shot,” Sylvia told me.

Sylvia considered posting the video to Facebook with a plea—“There’s a devil here shooting at Cielo Vista, come help!”—but decided against it, worried that the shooter would somehow see the video and find her under the McDonald’s table. “So,” she told me, “I thought, No, I’ll wait.” In all, she stopped and started three short videos, from the floor, beginning at 10:39 A.M. They capture legs running through the store; a person crouching by a cash register; another body prone under a McDonald’s table; a stunned man looking for his wife as an employee begs him to take cover; another body dropping, limply, in an aisle.

Sylvia showed all three videos to me, narrating what happened. At one point, she referred to the shooter as “that demon over there.” She added that she meant “demon” literally. A third clip showed the view that she had of their eventual escape route, through a side door, beckoned by a Walmart employee. “I said, ‘We need to get out of here.’ Mom said, “Quiero mi café.” (“I want my coffee!”) “She was in shock. I told her the shooter was maybe looking for more ammunition, we had to go.” As they left, leaning against each other for strength, they realized that they were the only people still in the restaurant.

Outside, she went on, “it was like a nightmare, like a horror movie: people running and crying all over.” A man in a blood-soaked shirt stumbled toward an ambulance. Their car was at the back of the lot, and her mother was having trouble moving, so they caught a short ride there. As Sylvia finally drove out of the lot, with her hands shaking, a police car, coming the other direction on a one-way street, missed striking hers by inches.

Back home, Sylvia collapsed in her room. She crawled under her sheets and picked up the phone. She called her adult son. Then she logged on to Facebook, where her online community waited. After resting for about forty-five minutes, she posted a clip from the shooting—the one taken under the table that did not show anyone dying. Alongside it, in Spanish, Sylvia wrote, “What a horrible experience!!!! Shooting in the Walmart at Cielo Vista!! My mom and I were under the table recording! 911 never answered! We are very grateful to Jehovah God for having taken care of us!!!” The video has since been shared thirty-three thousand times and drawn nearly six thousand comments on the social-media platform. It has been viewed nearly two million times.

Some of the earliest viewers of Saucedo’s video of the shooting were journalists. She was flooded with so many texts and calls and direct messages from the news media that she couldn’t keep track of texts from her family and friends. She turned off the notifications on her phone.

Among the first to discover her video and reach out to her, Saucedo said, was a local El Paso TV news station. It aired and then shared her video with “Good Morning America”—without her permission, she told me. Saucedo assumed that that was how things worked. She was picked up at three-forty-five the next morning, as requested by “Good Morning America” ’s producers, and, after hours of coaching, briefly appeared on the show. Following that appearance, Saucedo—or her video, or both—made their way to CNN, ABC, and Univision. She was interviewed by Jorge Ramos and David Muir—“very professional and handsome,” she said of both. She received calls, or was otherwise contacted, by reporters and producers from Serbia, the United Kingdom, Mexico, Colombia. A few offered her “a lot of money” for rights to the video, which she declined. “Every single channel reached out except Fox News,” she told me. (Days later, she offered to provide the videos to the F.B.I., and they looked through her phone, she said, despite her protests that she had personal photos and videos—of her recent attempts to lose weight—mixed in with the clips they were after.)