Note: This article was updated to reflect revised number of Mexican national victims and charges sought by prosecutors

As the dust begins to settle in El Paso, Texas – following one of the worst mass shootings in U.S. history – one element of the investigation has become increasingly clear to authorities: the shooter planned to kill Hispanics.

Saturday's massacre at a local Walmart supermarket left at least 20 people dead and 26 injured, making it the 250th mass shooting in 215 days according to the non-profit Gun Violence Archive, an organization that collects data on gun violence in the U.S.

Two law enforcement officials who spoke to The Associated Press on condition of anonymity identified the shooter as 21-year-old Patrick Crusius from Allen, Texas – about a 9-hour drive from El Paso.

Police said they arrested Crusius without incident shortly after the first rounds were fired. Now authorities are picking up a thread with the FBI investigating the shooting as domestic terrorism, particularly targeted against the Latino immigrant community.

"It has a nexus at this point in time to a hate crime. The FBI will be looking into that with other federal authorities," said El Paso Police Chief Greg Allen.

Manifesto

Authorities are trying to confirm a link between Crusius and an online 'manifesto' posted minutes before the attack, which detailed the alleged shooter's plan.

"This attack is a response to the Hispanic invasion of Texas," read the four-page diatribe reviewed by CGTN. The document expressed anti-immigrant, anti-government, and anti-corporate views.

"The manifesto narrative is fueled by hate and it's fueled by racism, and bigotry, and division," said Veronica Escobar, a congresswoman representing Texas.

The screed was quickly removed from 8chan, an online forum also used by the Christchurch gunman who targeted immigrants in a New Zealand mass shooting.

Victims

Although identities of the victims have yet to be released, Mexican Foreign Relations Secretary Marcelo Ebrard revealed 13 of them to be Mexican nationals; seven killed and six injured including a 10-year-old girl.

"It's a very unfortunate incident," said Mexico's President Manuel Lopez Obrador. "This is a result of a rotting problem some people suffer from." 

Read more: Mexico plans legal action over shooting of Mexicans in El Paso

Border community

The city of El Paso has roughly 680,000 residents, 83 percent of which are Hispanic, according to U.S. Census data. The Walmart where the shooting took place is four kilometers away from Ciudad Juarez, Mexico. The community shares deep roots and cultural and linguistic ties. 

It sits in stark contrast to Allen, Texas, which has a population of just over 100,000 residents, 61 percent of which are White and only 10 percent are Hispanic.

Locals tout El Paso as one with the lowest crime in the country. Home security and safety website Safewise ranks El Paso as the 6th safest city in 2019.

"In a city of almost 700,000 we have five murders in the entire year," said former Congressman from Texas and current Democratic Presidential candidate Beto O'Rourke. "The average over the last 10 years is 18. We exceeded that average just on one day. This is not normal; it is not acceptable."

"[El Paso is] a community that has shown nothing but generosity and kindness to the least among us; those people arriving at America's front door," noted Escobar.

Immigrant fear

Undocumented immigrants living in El Paso affected by Saturday's massacre may avoid seeking help due to their legal status in the U.S. and fears of being detained and later deported from the country.

“It’s clear there’s people who are not unifying with their family and that there are people they’re worried are injured that did not go to hospitals likely because of their immigration status,” Juliette Kayyem, a former assistant secretary for the U.S. Department of Homeland Security told CNN.

U.S. Customs and Border Protection, the agency tasked with enforcing immigration laws, tweeted it would deliberately avoid targeting the undocumented population in those sensitive locations.

Those still concerned about coming forward were offered other resources through pro-immigrant groups, such as the Hope Border Institute. 

U.S. President Donald Trump took to Twitter expressing his condolences to the victims of the Texas shooting.

"Today’s shooting in El Paso, Texas, was not only tragic, it was an act of cowardice. I know that I stand with everyone in this Country to condemn today’s hateful act," he said. "There are no reasons or excuses that will ever justify killing innocent people."

However, O'Rouke blasted Trump for his rhetoric on immigrants and called for gun reform as a solution to end mass shootings like the one in El Paso.

"President Trump's racism does not just offend our sensibilities; it fundamentally changes the character of this country. And it leads to violence," he said on Twitter.

Other prominent political figures are calling the Texas Walmart shooting an act of "white terrorism" including republican George P. Bush, Texas General Land Officer Commissioner and nephew to former President George W. Bush.

Former United States Deputy Attorney General Rod Rosenstein agreed, saying: "Many of the killers are lone-wolf losers indoctrinated to hate through the internet."

Authorities are working to notify next of kin and are expected to formally charge Crusius with capital murder in addition to other federal charges in the coming days.