Less than a week ago, 3 were killed at Gilroy Garlic Festival in California

Authorities are looking at an online writing to see if it's linked to suspect

Suspect is from Dallas suburb hours away from border town of El Paso

EL PASO, Texas — Twenty people were shot to death and 26 were wounded after a lone gunman went on a shooting rampage Saturday morning in a packed Walmart store in this border city, authorities said.

The suspect, identified by two law enforcement sources as Patrick Crusius, 21, of Allen, Texas, surrendered to officers and was being interviewed, police said. Allen is a suburb of Dallas, about 660 miles east of El Paso.

The first calls came in at 10:39 a.m. MDT, and the first officer arrived six minutes later in what would become a massive response, according to El Paso Police Chief Greg Allen.

Stay up on the latest:Everything we know about the victims, the suspect

With the shooting, a busy weekend shopping day turned into horror. The Walmart was "at capacity," and at a mall across the parking lot, 1,000 to 3,000 people were shopping, police Sgt. Robert Gomez said. Videos posted to social media show shoppers scrambling for cover, their hands raised.

The suspect, who is white and targeted a heavily Hispanic area, had posted a "manifesto" and the shooting was being investigated as a hate crime, Allen said. He gave no details about the contents of the manifesto.

El Paso, situated at the U.S.-Mexico border, is about 83% Hispanic, according to 2018 Census estimates, and boasts a large population of immigrants. The Mexican government said three Mexican citizens were killed and six were wounded.

Who is the suspect? What we know about the 21-year-old from Allen, Texas

The University Medical Center of El Paso received 13 victims, ranging in age from 2 to senior citizens, and one has died, the hospital said.

Del Sol Medical Center received 11 victims ages 35 to 82. Two are stable, nine are critical and three of those are in "a life-threatening predicament," the hospital said.

On Monday, the death toll rose to 22, with 24 injured.

Many people drove themselves or their loved ones to the hospital, Gomez said, adding to the confusion.

Blood donations were needed "urgently," police said on Twitter.

Walmart employee Leslie Diaz, 25, helping customers in a checkout line at the front of the store, said she heard multiple loud “pops” getting closer and louder, She said she looked at her coworkers, grabbed some customers and led them out of the store as customers began running and screaming toward the exit.

She said the store serves customers from both El Paso and those coming over from Chihuahua, Mexico.

Tabitha Estrada, 19, was at a GNC vitamin outlet at the front of the Walmart, when she heard customers screaming to get away. She led people in a room with a lock on the door and they stayed there, she said, until she heard officers shout: “Come out with your hands up!”

An hour after hiding, Estrada reunited with her mother, Rebeca Rivas, 40. They hugged and held each other,

“Mija, you’re alive,” Rivas said.

Families came to a reunification center at MacArthur Elementary School set up after the shooting searching for loved ones.

Patricia and Juan Menchaca had feared the worst. Their daughter and daughter-in-law had left their cellphones at home when they took the families shopping for back-to-school supplies. But at the center, they found that all were safe.

“They’re amazing,” a teary-eyed Patricia Menchaca said of those staffing the center.

Throughout the afternoon, dozens of local residents dropped off bottled water at the center. Erica Rios, who lives a few blocks from the school, was one of them

Rios’ grandmother had been on her way to the Walmart, where the family shops for groceries, minutes before the news broke.

“This is El Paso’s time to shine,” Rios said of the outpouring of volunteer support at the center. “We’re a united community.”

President Donald Trump responded on Twitter, calling the shootings an "act of cowardice" in one tweet and pledging the federal government's help in another. The FBI was taking part in the investigation.

Texas Gov. Greg Abbott weighed in as well.

"Texas grieves for the people of El Paso today. On a day that would have been a normal day for someone to leisurely go shopping turned into one of the most deadly days in the history of Texas," Abbott said at a press conference.

Local officials were stunned.

"This is a tragedy we would have never ever thought would happen in El Paso," El Paso Mayor Dee Margo said.

Former U.S. Rep. Beto O'Rourke, a Democratic candidate for president whose district included El Paso, was set to take part in a campaign event in Las Vegas when reports of the shooting came in.

“We have to find some reason for optimism and hope or else we can resign ourselves to a future where nearly 40,000 people a year will lose their lives to gun violence, and I cannot accept that,” O’Rourke said on stage in Las Vegas. He said he planned to return immediately to El Paso.

A family that was near Walmart during the shooting fled to a nearby Landry’s Seafood, hostess Sofia Cervantes told USA TODAY.

“They are in shock right now,” Cervantes said. “They were barely able to talk to us.”

The shooting comes just days after two people were shot and killed in a Walmart store in Southaven, Mississippi, south of Memphis, and the same week three people were killed at a shooting at the Gilroy Garlic Festival in California.

Contributing: Doug Stanglin, Kevin Johnson; Molly Smith, El Paso Times