The possibility that an anti-Hispanic motive might be behind the attack angered and startled residents and officials in the city of 682,000.
“This is about hate,” El Paso’s Democratic congresswoman, Representative Veronica Escobar, said in an interview.
Officials said it was too early to discuss possible motives, but Chief Allen said the attack “has the nexus at this point and time to a hate crime. The F.B.I. will be looking into that with other federal authorities.”
The F.B.I. is reviewing evidence to determine whether to move forward with federal charges, said Emmerson Buie Jr., the special agent in charge of the F.B.I. in El Paso. But he said that the bureau had not determined whether the shooting was a hate crime, an act of domestic terrorism or some other federal crime.
The Texas authorities said they were conducting a murder investigation, with the potential for other lines of inquiry.
Mr. Crusius lived with relatives in the Dallas suburb of Allen. In an upper-middle-class neighborhood of two-story homes with neatly manicured lawns, an F.B.I. agent was stationed outside the house and prevented reporters from knocking on the door. “We’re not sure if it’s secure yet,” the agent explained. State and federal officers later blocked the streets leading to the house.
Mr. Crusius appeared to live with his grandparents. A neighbor said he saw the couple’s grandson a few times, but the young man showed no abnormal behavior or appearance.
In El Paso on Saturday night, more than 200 people gathered at St. Pius X church for a vigil for the victims and their families. “Any of us could be dead right now — that’s how close it feels,” said Celina Arias, 44, a schoolteacher who attended the vigil. Her husband had been outside the Walmart putting gasoline in their car minutes before the gunman opened fire.
“I just want the families who are mourning to know they’re not alone,” she said. “It’s hard to imagine the pain they are experiencing.”
The gunfire on Saturday in El Paso began shortly before 11 a.m., in a popular commercial district with scores of restaurants and stores that are often crowded on the weekends. The Walmart store, near Hawkins Boulevard and Gateway Boulevard West, was packed at the time.
The timestamp on security-camera footage of the gunman walking in was 10:39:35. Chief Allen said the first officer on scene arrived six minutes later, at 10:45 a.m.
Sergio Armando Samaniego, 40, a clerk in the store’s garden center, said he believed the gunman entered through the automotive section. Mr. Samaniego had been on break and was headed back to the garden center when he heard gunshots.
“I’m lucky,” Mr. Samaniego said. “One of my friends was shot. I saw another customer running out of the store with a shot in his back. I’m just shocked.”
Victor Gamboa, 18, who works at the McDonald’s inside the Walmart, said he had heard shots and saw smoke. “I saw a man on the floor full of blood,” he said. “He appeared to be dead. It happened very quickly.”
Mr. Gamboa said he and other McDonald’s workers sheltered the customers to keep them safe and huddled on the ground for 15 minutes. Officers eventually arrived and escorted the group out to a Sam’s Club store across the street.
Victor Guerrero, a spokesman for Del Sol Medical Center in El Paso, said the hospital was treating 11 victims ranging in age from 35 to 82. Nine were in critical but stable condition and two were stable.
The University Medical Center of El Paso received 13 patients, according to Ryan Mielke, the hospital’s spokesman. He said two minors, including a 2-year-old, had been stabilized and transferred to El Paso Children’s Hospital.
State Representative Cesar Blanco, whose district includes the Walmart, was at home when he heard about the attack. Mr. Blanco, a Democrat and Navy veteran, rushed to his district office, which is near the mall, and later joined other officials in assisting grief-stricken families at an emergency center set up at a middle school where Mr. Blanco was once a student. About 50 to 75 family members were gathered in the school cafeteria, he said.
“Right now the families are in shock,” Mr. Blanco said, describing the sounds of “wailing and screams” from family members whose loved ones were among the victims. “This is terrorism. This is domestic terrorism.”
Beto O’Rourke, the Democratic presidential candidate and former Texas congressman who represented El Paso for years, canceled his campaign events in Nevada and California to return to the city. On Saturday, speaking at a Las Vegas candidates’ forum before he departed for El Paso, Mr. O’Rourke teared up.
“A lot of injury, a lot of suffering in El Paso right now,” he told the audience. “I’m incredibly sad and it’s incredibly hard to think about this. Very hard to think about this, but I’ll tell you, El Paso is the strongest place in the world.”
Frida Murga, a student at the University of Texas at El Paso, was at a town hall meeting hosted by Ms. Escobar, the congresswoman, at Coronado High School when news of the shooting was announced.
“A man had actually just asked Congresswoman Escobar to let the president of the N.R.A. know that he wanted to debate him on gun violence,” Ms. Murga said. The man was a veteran and said he did not value guns more than lives.
One by one, police officers at the town hall left, and one of the staff members approached the congresswoman to let her know the police wanted everyone to evacuate.
“I didn’t realize it would be this serious,” Ms. Murga said.