A shooting at at a sprawling shopping complex in El Paso on Saturday left at least 20 people dead, Texas Gov. Greg Abbott said.
More than two dozen people were injured in the shooting at Walmart, where some of the chaos was caught on camera and showed victims lying in the parking lot.
Police say they have a 21-year-old man in custody in connection with the shooting.
Here's what we know:
Where the shooting took place
The shooting took place at the Walmart, near the Cielo Vista Mall, Sgt. Robert Gomez, an El Paso police spokesman, told reporters.
Police began receiving reports of an active shooter around 10 a.m. (noon ET). Police received multiple calls from stores at the mall complex, where Walmart sits.
In a shaky Snapchat video aired by CNN, a woman holding the camera runs through a mall department store and into a parking lot.
As the group hurries past racks of clothes and cases of merchandise, voices off camera shout, 'Hands up!'
Another video, shot from outside the Walmart, showed people lying on the ground, some of them next to a table set up by the store's entrance.
'There's a man lying down at the stand that a school set up,' the man holding the camera says in Spanish.
'Help!' a man screams in English.
'We need CPR,' someone else says. 'We need CPR.'
Gomez said it's estimated that up to 3,000 shoppers and 100 employees were inside the Walmart at the time of the shooting.
How many victims there are
At least 20 people were killed in what was 'one of the deadliest days in the history of Texas,' Abbott said Saturday evening during a press conference.
The victims have not been publicly identified, with authorities citing the investigation and pending next of kin notifications.
Three Mexicans were among those killed, Mexico President Andrés Manuel López Obrador said via Twitter.
At least 26 people were wounded, El Paso Police Chief Greg Allen said. Of the wounded, 23 were taken to two area hospitals, two hospital spokesmen told CNN. Six Mexicans were among the injured, Mexico Secretary of Foreign Affairs Marcelo Ebrard said via Twitter.
Thirteen people were taken to the University Medical Center of El Paso, where one died, medical center spokesman Ryan Mielke said.
Another 11 people were taken to Del Sol Medical Center, according to spokesman Victor Guerrero. Dr. Stephen Flaherty said the patients were between the ages of 35 and 82.
At least two patients at Del Sol are in a 'life-threatening predicament,' Flaherty said later at a press conference.
Nine patients were in critical condition, Flaherty said. Of those, he said seven patients required emergency operations. He said most of the patients will likely need more procedures in the coming days.
Who carried out the shooting
The suspect in the deadly shootings at the shopping complex has been identified as Patrick Crusius, 21, of Allen, Texas, three sources told CNN.
The information provided to CNN came from two federal law enforcement sources and one state government source. The federal sources told CNN that investigators are reviewing writing posted online days before the shootings that may speak to a motive.
The sources say the online posting was believed to be written by Crusius, but that has not been confirmed.
The police chief did not identify the suspect during a press conference Saturday evening, but Allen did say the shooter was a 21-year-old white man from Allen, Texas. The suspect faces possible capital murder charges, he said.
Allen said the shooter surrendered to officers when they approached him in Walmart.
Collin College, northeast of Dallas, confirmed in a written statement that Crusius was a student there from 2017 to 2019.
'Collin College is prepared to cooperate fully with state and federal authorities in their investigation of this senseless tragedy. We join the governor and all Texans in expressing our heartfelt concern for the victims of the shooting and their loved ones,' College President Neil Matkin said.
Where the investigation stands
The FBI has opened a domestic terrorism investigation into the shooting, a source familiar with the investigative process told CNN.
Initial reports were that the weapon used in the shooting was a rifle, El Paso Police Sgt. Enrique Carillo told reporters during an earlier news briefing.
The FBI in El Paso took to Twitter to ask anyone who took video or pictures during and after the shooting to submit them to investigators.
The crime scene will 'be in play for a long period,' Allen said. 'Unfortunately, the deceased will remain at the scene until the scene is processed properly for evidentiary purposes to be gathered for later prosecution.'
The shooting is being investigated as a murder, but authorities say there are some aspects that indicate the possibility of a hate crime.
'Right now, we have a manifesto from this individual that indicates to some degree that it has a nexus to a potential hate crime,'Allen said.
The FBI cautioned the investigation is still in its early stages, and more work needs to be done to determine if it was a hate crime.
'There is potential for a number of different other violations, and we're reviewing all the evidence to make a determination as to what potentially else is out there, in addition to the violations that have been stated that the local authorities are pursuing,' FBI El Paso Agent in Charge Emmerson Buie said during Saturday evening's news conference.
Law enforcement officials are investigating a four-page document posted to 8chan that they believe was written by Crusius. 8chan is an online message board rife with racist and anti-Semitic conspiracy theories.
The document was attached to a post on 8chan that said, 'I'm probably going to die today.' A CNN analysis of the 8chan post found it was posted less than 20 minutes before police received the first calls about the shooting.
The document is filled with white nationalist and racist hatred toward immigrants and Hispanics, blaming immigrants and first-generation Americans for taking away jobs and the blending of cultures in the US.
The writer discussed fears of an influential Hispanic population in Texas that would make the state a 'Democratic stronghold,' though it also said 'the Republican Party is also terrible,' because the Republican Party is pro-corporation, which can lead to more immigration. The writer also wrote opinions on immigration the predate President Trump, and the writer appears to have held these beliefs for years.
The post further says the writer took less than a month to plan the shooting and describes the weapons used.
Facebook says it is working with law enforcement. Facebook and Instagram profiles under the suspect's name have been removed by the company.
Facebook and Twitter say they are working to prevent people from sharing the document.
Despite the companies' claims that they are removing the writings, CNN was easily able to find multiple versions of the writings on the platforms.
'We're proactively removing content that violates our policies and will be engaged with law enforcement, as appropriate,' a Twitter spokesperson said.
Facebook said it was taking similar action.
'Content that praises, supports or represents the shooting or anyone responsible violates our Community Standards, and we will continue to remove as soon as we identify it,' a Facebook spokesperson said.
Google, which owns YouTube, did not immediately respond to CNN's request for comment.
Attorney General William P. Barr offered the Justice Department's full support.
'Those who commit such atrocities should be held accountable swiftly and to the fullest extent the law allows,' Barr said in a statement.
What officials are saying
Abbott vowed to see justice done.
'We are going to aggressively prosecute it both as capital murder, but also as a hate crime, which is exactly what it appears to be without having seen all the evidence yet,' Abbott said. 'We have to be very, very clear that conduct like this, thoughts like this, actions like this, crimes like this are not who or what Texas is and will not be accepted here.'
El Paso Mayor Dee Margo said during the press conference that the city will stay united despite the tragedy.
'Our community will not be defined by this senseless evil act of violence,' Margo said. 'United our community will heal. El Paso is too strong to be broken by a cowardly act like this.'
President Donald Trump has been briefed on the shooting, and the White House is monitoring the situation, deputy press secretary Steven Groves said.
'Today's shooting in El Paso, Texas was not only tragic, it was an act of cowardice,' Trump said on Twitter. 'I know that I stand with everyone in this Country to condemn today's hateful act. There are no reasons or excuses that will ever justify killing innocent people ... Melania and I send our heartfelt thoughts and prayers to the great people of Texas.'
Democratic presidential candidate Beto O'Rourke, who is from El Paso, pulled out of presidential forum in Las Vegas to head back to Texas.
'I'll tell you, El Paso is the strongest place in the world. This community is going to come together. I'm going back there right now to be with my family and my hometown,' he said.
Walmart CEO Doug McMillon released a statement on Instagram saying he couldn't believe he had to send a note like this 'twice in one week.' Another shooting at Walmart occurred this week in Mississippi and left two people dead.
'My heart aches for the community in El Paso, especially for the associates and customers at store 2201 and the families of the victims of today's tragedy. I'm praying for them and I hope you will join me,' McMillon said.
Immigration officials in El Paso, which sits on the US-Mexico border pledged their support to the community.
Hector Mancha, US Customs and Border Protection El Paso director of field operations, and Gloria Chavez, US Border Patrol El Paso sector interim chief patrol agent, released a statement on behalf of both agencies on Twitter.
'El Paso is our home and we offer any assistance we can today and beyond,' the statement read. 'On behalf of the men and women of CBP, our thoughts and prayers are with those affected by this senseless violence.'
The shooting also renewed the debate on gun control.
House Speaker Nancy Pelosi said the shooting was horrific and 'breaks the hearts of all Americans.'
'Too many families in too many communities have been forced to endure the daily horror of gun violence. Enough is enough. The Republican Senate's continued inaction dishonors our solemn duty to protect innocent men, women and children and end this epidemic once and for all,' Pelosi said in a statement.
Sen. Chuck Schumer, D-New York, said on Twitter: 'We must act to help end gun violence in America.'
GOP Sen. Lindsey Graham, of South Carolina, tweeted the shooting was 'sick and senseless.'
'Time to do more than pray. Time to enact common-sense legislation in Congress to empower states to deal with those who present a danger to themselves and others -- while respecting robust due process,' Graham said. 'May not have mattered here, but Red Flag laws have proven to be effective in states that have them.'