EL PASO — A mass shooting at a Walmart in this border city killed 20 people and left more than two dozen others injured Saturday, and police arrested a 21-year-old North Texas man who they said may have written a manifesto revealing that the crime was racially motivated.

El Paso Police Sgt. Robert Gomez said police arrested the man without incident near the Walmart next to Interstate 10 on the east side of the city. Gomez did not identify the man, but CNN and other news outlets, citing multiple sources, have identified him as 21-year-old Patrick Crusius of Allen, north of Dallas — more than 650 miles from El Paso.

Gomez said police don't believe there were other shooters — but he said they are still investigating.

"This is unprecedented in El Paso," Gomez said.

El Paso Police Chief Greg Allen said that "the scene is a horrific one" and added that the FBI will be investigating whether it was a hate crime. Allen mentioned a manifesto that suggests a hate crime, adding that investigators will study whether the shooter wrote it. FBI Special Agent in Charge Emmerson Buie said the agency is reviewing "all the evidence that we have collected so far." CNN reported that the FBI has opened a domestic terror investigation in the case.

In a statement to CNN, Gov. Greg Abbott called the shooting "disgusting, intolerable ... we are going to prosecute it as capital murder but also as a hate crime."

"We must do one thing today, one thing tomorrow and each and every day after this," he said at an earlier press conference. "We must unite. ... Now is the time for Texans to come together to support each other, to help these families in need and make sure that El Paso takes the step forward that it needs to take."

When pressed about what lawmakers could do to prevent yet another mass shooting in Texas, Abbott highlighted legislation passed this year that he said addressed school safety and mental health issues that arose after the deadly shooting at Sante Fe High School last year.

"That [shooting] led to three days of hearings that I conducted at the Capitol to get input from people who are educators, who are students, who are victims of shooting crimes, as well as experts in all different kinds of fields to help us be able to strategize the best ways to keep students safe and to prevent incidents like that from happening again," he said. "During that time we did not, as far as I know, evaluate for and plan for an incident like this. That said, I can tell you that perhaps the most profound and agreed upon issue that came out of all of those hearings was the need for the state and for society to do a better job of dealing with challenging mental health based issues."

U.S. Rep. Veronica Escobar, D-El Paso, who also spoke at the press conference, said placing the blame on mental health issues alone isn’t good enough.

“We have failed. We have failed this state and we have failed our country," Escobar said. "Putting it on mental health care alone, lack of access to mental health care, that’s not right.”

Gomez said 911 calls about the shooting began coming in at 10 a.m. local time. Law enforcement soon sealed off the area around the Walmart. FBI SWAT teams could be seen near armored vehicles, along with Texas Department of Public Safety troopers, as a military-style helicopter circled overhead.

A spokesman for El Paso University Medical Center told CNN that 13 shooting victims were transported to the hospital and one later died. The hospital’s CEO later told the network that the victims ranged in age from 35 to 82 years old and nine were in critical condition.

Victoria Hankins, a 38-year-old El Paso native, said she was in the grocery area near the rear of the store when she heard seven or eight shots in rapid succession. She said everyone hit the floor and started crawling away from the shots. Hankins said someone told them to hide in the back of the store, and a number of people crowded into a metal shipping container, which was stifling in the heat. She said people in the store helped each other find places to hide.

When they emerged after the shooting was over, Hankins said she saw a woman exit the store with blood on her legs, saying she was looking for her children.

"I'm not surprised by everyone taking care of each other inside," Hankins said, adding that she also wasn't surprised that someone would start shooting inside the Walmart. "It can happen anywhere nowadays. It's crazy."

Another survivor, who would only give his first name, Raul, said he was inside the Walmart and heard several rapid-fire shots. He said he was instructed to get out of the store, then became stranded because his truck was inside the crime scene perimeter.

Gaby and Lorenzo were inside the Walmart in #ElPaso where there is an active shooter. They say they saw at least 5 shot. https://t.co/FqHdnfeu5U — Ivan Pierre Aguirre (@i_p_a_1) August 3, 2019

It's the third mass shooting in Texas in less than two years. In November 2017, a mass shooting at a church in Sutherland Springs, a small community about 30 miles southeast of San Antonio, left 26 people dead and 20 wounded. The 26-year-old gunman died after fleeing the scene when citizens exchanged gunfire with him. And in May 2018, a shooter killed 10 people and wounded 13 others at Santa Fe High School outside of Houston.

"We are all trying to piece together what has happened in our community," Escobar told CNN. "It is unfathomable.

“And it is unfortunately an all too common pain across America," Escobar added. "We have the solutions. They are right in front of us. What we need is the will to act as a country."

Texas Attorney General Ken Paxton said his office would help all law enforcement agencies involved in the shooting investigation. "Our deepest sympathies and prayers extend to all the people of El Paso, especially those who have been directly impacted by this tragedy," Paxton said in a written statement.

President Donald Trump tweeted, "Terrible shootings in ElPaso, Texas. Reports are very bad, many killed. Working with State and Local authorities, and Law Enforcement. Spoke to Governor to pledge total support of Federal Government. God be with you all!"

But former El Paso Democratic congressman and current presidential candidate Beto O'Rourke said Trump's rhetoric has contributed to the rise of racism in the country.

"We also have to ask ourselves about the level of hatred and racism we’re seeing in this country right now," O'Rourke said in a Facebook livestream. "We’ve had a rise in hate crimes every single one of the last three years during an administration where you have a president who’s called Mexicans rapists and criminals, though Mexican immigrants commit crimes at a far lower rate. He’s tried to make us afraid of them."

U.S. Sen. Ted Cruz of Texas issued a written statement, saying, "My heart is with everyone in El Paso struck by this unspeakable evil. Heidi and I are praying for the victims and their families and grateful for the first responders, local authorities, and law enforcement officers working tirelessly to bring the perpetrator of this depraved act to justice and keep the entire community safe. There are millions of people in Texas and across the country standing behind you."

Lt. Gov. Dan Patrick said, "Texans are heartbroken over the news of the horrific shooting in El Paso. Please join Jan and I in praying for the city of El Paso, the victims, their families and their friends who have suffered an unspeakable loss today."

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