The Texas gunman who murdered 19 children and two teachers posted on Facebook that he was going to shoot up an elementary school about 15 minutes before his rampage, Governor Greg Abbott said, as harrowing details about the attack continue to emerge.
The gunman, identified as 18-year-old Salvador Ramos, also posted a message saying he was going to shoot his grandmother, as well as another one confirming that he had done so, Abbott said at a news conference.
His grandmother, whom Ramos shot in the face shortly before attacking the school, survived and called police.
Ramos fled the home he shared with his grandparents and crashed his car near Robb Elementary School in Uvalde, Texas. He entered the school through a backdoor carrying an AR-15 assault-style rifle and wearing tactical gear.
He barricaded himself in a fourth-grade classroom, authorities said, and killed students and teachers before he was fatally shot by a US Border Patrol officer. An additional 17 people suffered non-life-threatening injuries.
The Facebook posts were the only advance warning of the rampage, Abbott said, adding that Ramos did not appear to have any criminal record or history of mental health problems.
Ramos purchased two rifles and hundreds of rounds of ammunition days before the attack, several news outlets reported, citing a state senator who had been briefed by law enforcement.
The attack, which came 10 days after an avowed white supremacist shot 13 people at a supermarket in a mostly black neighbourhood of Buffalo, has reignited a national debate over US gun laws.
In a sign of the charged political atmosphere, Beto O'Rourke, the Democratic gubernatorial candidate challenging Abbott in a November election, interrupted the news conference to confront Abbott for loosening, rather than restricting, the state's gun laws.
Several officials yelled at O'Rourke, with one calling him a "sick son of a b*tch" for making the shooting a "political issue," though it was not clear who.
O'Rourke was escorted out of the building and spoke to reporters outside, calling it "insane" that an 18-year-old was legally permitted to acquire an AR-15.
"We can get that done if we had a governor that cared more about the people of Texas than he does this own political career or his fealty to the NRA," he said, referring to the National Rifle Association, a gun-rights advocacy organisation.
Texas has some of the country's most permissive firearm laws.
The idea that an 18-year-old can walk into a store and buy assault weapons is just wrong.
What in God’s name do you need an assault weapon for except to kill someone?
— President Biden (@POTUS) May 25, 2022
In a prime-time address on Tuesday evening, US President Joe Biden called for new gun safety restrictions.
"As a nation, we have to ask when in God's name we're going to stand up to the gun lobby," he said, his voice rising.
But new legislation appeared unlikely to pass in Washington. Virtually all Republicans in Congress oppose new gun restrictions, citing the US Constitution's guarantee of a right to bear arms, and there was no sign the massacre would alter that position.
White House officials were planning a trip to Texas for Biden, a senior administration official said.