UVALDE: The Texas gunman who murdered 19 children and two teachers posted an online message warning that he was going to shoot up an elementary school minutes before he attacked, Governor Greg Abbott said on Wednesday, as more harrowing details about Tuesday's rampage emerged.

The gunman, 18-year-old Salvador Ramos, also sent a message on Tuesday saying he was going to shoot his grandmother and another one confirming he had done so, Abbott said at a news conference. Ramos' grandmother, whom the suspect shot in the face shortly before attacking the school, survived and called police.

Ramos gave no warning except the online posts. After shooting his grandmother, he fled the home they shared and crashed his car near Robb Elementary School in Uvalde, Texas, about 80 miles (130 km) west of San Antonio.

A school police officer approached him outside the building, according to officials, but no gunfire was exchanged. Authorities offered few additional details of that encounter, which is likely to become a focus of investigations, except that the suspect dropped a bag full of ammunition on the ground and ran toward the school when he saw the officer.

Ramos then entered the school through a back door carrying an AR-15-style rifle and made his way down two hallways to a fourth-grade classroom where he shot all of the people who were killed. Authorities said he had legally purchased two rifles and 375 rounds of ammunition days before the shooting.

Meanwhile, police surrounded the building, breaking windows to help children and staff escape. U.S. Border Patrol agents also responded and entered the building to confront the shooter, with one agent wounded "in the crossfire," the Department of Homeland Security said on Twitter.

Eventually, Ramos, a high school dropout with no known criminal record or history of mental illness, was shot and killed by law enforcement.

Abbott said 17 people suffered non-life-threatening injuries, including "multiple children" who survived the gunfire in their classroom, according to Chris Olivarez, a Texas Department of Public Safety spokesperson.

The posts were made on Facebook, the governor said, but spokespeople for Facebook's parent company, Meta Platforms FB.O, said they were private one-to-one messages discovered after the shooting. The company declined to say who received the messages or which of Meta's platforms, such as Messenger or Instagram, was used to send them.

GUN CONTROL DEBATE

Investigators have not publicly identified a motive for what now ranks as the deadliest U.S. school shooting in nearly a decade. Ten days earlier an avowed white supremacist shot 13 people at a supermarket in a mostly Black neighborhood of Buffalo, New York, has reignited a national debate over U.S. gun laws.

In a sign of the charged political atmosphere, Beto O'Rourke, the Democratic candidate challenging Abbott in a November election, interrupted the news conference to confront Abbott over the state's permissive gun laws, shouting "You are doing nothing!"

Several officials gathered on stage around the governor yelled at O'Rourke. "You're a sick son of a bitch who would come to a deal like this to make a political issue," one of them said, though it was not clear who.

O'Rourke was escorted out of the building and spoke to reporters outside. He said it was "insane" that an 18-year-old was legally permitted to acquire a semi-automatic rifle and vowed to pursue gun restrictions.

"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 organization.

Abbott said stringent gun laws do not prevent violence, citing states such as New York. He said policymakers should instead focus on mental health treatment and prevention.

In a prime-time address on Tuesday evening, 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 gun restrictions, 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.

The NRA's annual meeting starts on Friday in Houston, where Republicans including Abbott, Texas U.S. Senator Ted Cruz and former President Donald Trump are all scheduled to speak.

In a statement, the NRA expressed sympathy for the victims but said the event would go on as planned.

World leaders expressed shock and sorrow. Pope Francis on Wednesday said he was "heartbroken" and called for an end to "the indiscriminate trafficking of weapons." 

The head of the U.N. children's agency UNICEF, Catherine Russell, condemned the epidemic of U.S. gun violence, comparing it to attacks on schools in Afghanistan, Ukraine and West Africa and blaming government leaders for inaction.

Shootings have become so commonplace in American schools that data shows a gun being fired almost every day this year on school property, according to the K-12 School Shooting Database at the Naval Postgraduate School's Center for Homeland Defense and Security. 

The Texas rampage stands as the deadliest U.S. school shooting since a gunman killed 26 people, including 20 children, at Sandy Hook Elementary School in Connecticut in December 2012.

'I WILL MISS YOUR LAUGH FOREVER'

Uvalde, deep in the state's Hill Country region, has about 16,000 residents, nearly 80% of them Hispanic or Latino, according to U.S. Census data.

As community members set up fundraisers for the families of the victims, some relatives mourned their loved ones on social media.

"My little love is now flying high with the angels above," Angel Garza, whose daughter, Amerie Jo Garza, was killed, wrote on Facebook. "Please don't take a second for granted. Hug your family. Tell them you love them."

The two staff members killed were identified as Eva Mireles and Irma Garcia, fourth-grade teachers trapped in the classroom with their students when the shooting began.