EL PASO — The attack on a Walmart and shopping center here, during which a gunman killed 20 people and wounded dozens, is being viewed as a domestic terrorist attack, authorities said Sunday.

Federal authorities are “seriously considering” bringing hate crime charges in the case, John F. Bash, the U.S. attorney for the Western District of Texas, said Sunday. Those charges could carry the death penalty. Local prosecutors also say they plan to seek a death sentence in the case.

“We are treating it as a domestic terrorism case, and we’re going to do what we do to terrorists in this country,” Bash said. “Which is deliver swift and certain justice.”

The investigation in Texas continued while other authorities rushed to respond to a shooting just hours later in Dayton, Ohio, during which at least nine people were slain. The dual shootings in Texas and Ohio — separated by hundreds of miles and less than a single day — sparked grimly familiar scenes of panic and grief as public places were yet again terrorized by a hail of bullets.

It was a ghastly weekend in America, with more than two dozen people killed in the two shooting rampages over the course of a single tragic day. An additional seven people were wounded early Sunday during a shooting in Chicago.

Authorities in Ohio said an attacker wearing body armor there opened fire early Sunday morning amid a busy scene of bars and restaurants in a historic Dayton district. The shooter took less than a minute to carry out the carnage, officials said, before he was killed by police. Officials identified that gunman as a 24-year-old and said that among the victims was his sister. Another 27 people were injured, they said.

The rampage in El Paso hours earlier apparently began outside the Walmart on Saturday morning. A routine morning gave way to scenes of people screaming, running and dodging bullets in parking lots. One witness said the attacker was just “shooting randomly.”

Law enforcement authorities have delved into the background of 21-year-old Patrick Crusius, whom two officials identified as the suspect in the shooting here.

Crusius, from the Dallas suburb of Allen, surrendered to police, giving officials a relatively unusual chance to directly interrogate a mass shooting suspect. In many cases, attackers are killed or take their own lives; last week, a gunman opened fire on a food festival in Gilroy, Calif., fatally shooting three people, and then killed himself.

What prompted Crusius to travel to El Paso from the Dallas area remained unclear late Sunday, as did what prompted the gunfire at the Walmart to stop. But since being taken into custody, police said, Crusius has been cooperative, though they declined to go into detail about what he may have said.

“He was forthcoming with information,” Greg Allen, the El Paso police chief, told reporters. “He basically didn’t hold anything back. Particular questions were asked and he responded.”

There is no universally agreed upon definition of a mass shooting. Federal law defines a mass killing as three or more people killed in a single incident, a definition the FBI has cited in studies of active shooters. Other attempts to track the number of shootings, such as the online Gun Violence Archive, include cases in which multiple people were shot but not killed.

Authorities in Texas filed a capital murder charge against Crusius, according to court records, and he was booked into the downtown El Paso jail. No attorney was listed in those records as of Sunday; the public defender’s office did not respond to messages about whether it had been appointed to represent him.

Jaime Esparza, the El Paso district attorney, said the capital murder charge is eligible for a possible death sentence and left no question about what prosecutors would pursue.

“We will seek the death penalty,” Esparza said Sunday. “The loss of life is so great. We certainly have never seen this in our community. ... This community is rocked, shocked and saddened by what has happened here.”

Federal charges, when ultimately filed, would not supersede any charges brought by local prosecutors in Texas, but would instead operate as a parallel prosecution.

The shooting in El Paso set off waves of anger, sadness and recriminations, fueling calls for stricter gun control as the country reeled from yet another bullet-riddled rampage in yet another city.

What may have motivated the attacker remained a focus of investigators, who have examined a manifesto posted online that included screeds against immigrants. Authorities believe the Texas shooting suspect posted the document, officials said, but continue to gather evidence.

The manifesto was another unsettlingly familiar part of the tragedy. It listed angry — and, at times, jumbled — motivations for the attack, including rants about a “Hispanic invasion.”

El Paso Sheriff Richard Wiles, who oversees the jail holding the suspect, called the attack racist in a Facebook post Saturday night.

“This Anglo man came here to kill Hispanics,” he wrote. “I’m outraged and you should be too. This entire nation should be outraged. In this day and age, with all the serious issues we face, we are still confronted with people who will kill another for the sole reason of the color of their skin.”

The mood in El Paso turned from shock on Saturday to anger on Sunday as it seemed increasingly likely that a man had driven nine hours to kill people because they were Hispanic.

At a news conference by immigration advocates and community leaders, immigration attorney Carlos Spector placed blame for the attack at the White House.

“What is responsible for this is the racist language of Donald Trump," Spector said. “Since he was elected the Mexican community in the border has been in his gun sights.”

Former congressman Beto O’Rourke (D), who is running for president, appeared on “This Week" from his hometown of El Paso and said that Trump “doesn’t just tolerate -- he encourages this type of open racism.”

Acting White House chief of staff Mick Mulvaney on Sunday defended Trump, disputing that politics were connected with the shooting. Also appearing on “This Week," Mulvaney blamed the shooting on “sick people” and distancing Trump’s rhetoric from the attacker.

The scene after a shooting at an El Paso shopping center

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Aug. 6, 2019 | Yamileth Lopez holds a photo of her deceased friend, Javier Amir Rodriguez, 15, at a makeshift memorial for victims outside the Walmart, near the scene of the mass shooting in El Paso, Tex. (Mario Tama/Getty Images)

The manifesto found by investigators carried tragic echoes of previous attacks. The alleged shooter in Pittsburgh last year also ranted about an “invasion” before opening fire there. And the manifesto in Texas also referenced the alleged New Zealand attacker who opened fire in mosques there this year, killing 51 people, who had posted a manifesto citing a previous mass shooter in the United States.

Mass violence is often followed by the revelation that the suspected attacker studied or otherwise cited a previous attack — creating a tapestry of tragedy that has linked attacks in Florida and Virginia as well as others in South Carolina and New Zealand. The manifesto posted by the alleged New Zealand gunman specifically cited the white supremacist who attacked a church in Charleston, S.C., in 2015, killing nine black parishioners.

The shooting in El Paso was also the latest aimed at a soft target — places that, unlike highly secured government buildings, attract large crowds but can be relatively easily infiltrated by an attacker intent on carrying out violence. The Department of Homeland Security earlier this year released a document with guidance for security at such places, noting that they “may be vulnerable to attacks using simple tactics and readily accessible weapons.” This guide specifically mentioned shopping centers as possible targets.

The shooting in El Paso was the deadliest mass shooting in the country since November 2017, when a gunman killed 26 people in a church in Sutherland Springs, Tex. It also came a little more than a year after a gunman in Santa Fe, Tex., opened fire, killing 10 people at a high school.

Dolores Oñate and her husband, Roy Diaz, of South Carolina, returned to the area near the Walmart on Sunday morning to get their vehicle, which held their clothes, passports, medicine, money and other possessions. They had gone to the Walmart on Saturday morning with Diaz’s sister to buy supplies for their drive to Cuauhtemoc, in the Mexican state of Chihuahua, about four hours south of El Paso to visit Diaz’s father.

Oñate said she heard what sounded like something falling, then saw people running.

“I didn’t know what was going on until somebody said there’s a shooter,” she said.

On Sunday, police said that vehicles in the parking lot would have to remain there “for several days as they are part of the crime scene" which could potentially cause issues for people across the area.

Stephen Flaherty, the trauma medical director at Del Sol Medical Center, described the difficult work of trying to save lives after the shooting.

“It was a long night,” he told reporters. “It was a long day."

He praised the many people who came out to donate blood, saying that was critical. Flaherty also said that he expects a number of victims will need to return to the operating room in the coming days.

The attack reverberated beyond America’s borders. Mexico’s foreign minister expressed outrage Sunday at the killings in El Paso and said his government would announce legal action to protect the Mexican and Mexican American communities in the United States.

Foreign Minister Marcelo Ebrard said a number of Mexicans had been killed in the attack — although he did not specify the number — and nine wounded.

“Mexico declares its profound rejection and complete condemnation of this barbaric act, in which innocent Mexican men and women lost their lives, and nine [Mexicans] were wounded,” Ebrard said in a recorded message on his Twitter feed.

The minister said his government’s first priority was to help the victims and the second was to pursue “legal actions that are efficient, quick, expedited and complete,” to ensure that “conditions are in place to protect the Mexican American community, and Mexican men and women in the United States. What has happened is unacceptable.”

Berman reported from Washington. Hannah Knowles, Devlin Barrett, Jennifer Jenkins and Julie Tate in Washington; Mary Beth Sheridan in Mexico City; and Alexandra Hinojosa in El Paso contributed to this report, which is being updated regularly.