The archbishop of San Antonio, Gustavo Garcia-Siller, comforts families outside the Civic Center following a deadly school shooting at Robb Elementary School in Uvalde, Texas, on Tuesday. (Associated Press)

The gunman who massacred 19 children and two teachers at an elementary school in Texas warned in online messages sent minutes before the attack that he had shot his grandmother and was going to shoot up a school, the governor said Wednesday.

Salvador Ramos, 18, used an AR-15-style semi-automatic rifle in the bloodshed Tuesday at Robb Elementary School in Uvalde, which ended when police stormed a classroom and killed him. He legally bought the rifle and a second one like it last week, just after his birthday on May 16, authorities said.

“Evil swept across Uvalde yesterday. Anyone who shoots his grandmother in the face has to have evil in his heart,” Gov. Greg Abbott said. “But it is far more evil for someone to gun down little kids.”

Investigators shed no light on the motive for the attack, which also left at least 17 people wounded. The governor said Ramos, a resident of the small town about 85 miles west of San Antonio, had no known criminal or mental health history.

But about a half-hour before the mass shooting, Ramos sent the first of three messages online, Abbott said. Ramos wrote that he was going to shoot his grandmother, then that he had shot the woman. In the last note, sent about 15 minutes before he reached Robb Elementary, he said he was going to shoot up an elementary school, according to Abbott. Investigators said Ramos did not specify which school.

Ramos sent private, one-to-one text messages via Facebook, and they were “discovered after the terrible tragedy,” company spokesman Andy Stone said. He said Facebook is cooperating with investigators.

As details of the latest mass killing to rock the U.S. emerged, grief engulfed Uvalde, population 16,000.

The dead included Eliahna Garcia, an outgoing 10-year-old who loved to sing, dance and play basketball; a fellow fourth-grader, Xavier Javier Lopez, who had been eagerly awaiting a summer of swimming; and a teacher, Eva Mireles, with 17 years’ experience whose husband is an officer with the school district’s police department.

“You can just tell by their angelic smiles that they were loved,” Uvalde Schools Superintendent Hal Harrell said, fighting back tears as he recalled the children and teachers killed. “That they loved coming to school, that they were just precious individuals.”

Amid calls around the U.S. for tighter restrictions on firearms, the Republican governor repeatedly talked about mental health struggles among Texas young people and argued that tougher gun laws in Chicago, New York and California are ineffective.

Democrat Beto O’Rourke, who is running against Abbott for governor, interrupted Wednesday’s news conference, calling the tragedy “predictable.” Pointing his finger at Abbott, he said: “This is on you until you choose to do something different. This will continue to happen.” O’Rourke was escorted out as some in the room yelled at him, with Uvalde Mayor Don McLaughlin calling him a “sick son of a bitch.”

Texas has some of the most gun-friendly laws in the nation and has been the site of some of the deadliest shootings in the U.S. over the past five years.

“I just don’t know how people can sell that type of a gun to a kid 18 years old,” Siria Arizmendi, the aunt of victim Eliahna Garcia, said angrily through tears. “What is he going to use it for but for that purpose?”

Lt. Christopher Olivarez of the Texas Department of Public Safety told CNN that all of those killed were in the same fourth-grade classroom.

The killer “barricaded himself by locking the door and just started shooting children and teachers that were inside that classroom,” Olivarez said. “It just shows you the complete evil of the shooter.”

Police and others responding to the attack also went around breaking windows at the school to enable students and teachers to escape. Officers eventually broke into the classroom and killed Ramos in one last exchange of gunfire, authorities said.

The attack in the predominantly Latino town was the deadliest school shooting in the U.S. since a gunman killed 20 children and six adults at Sandy Hook Elementary in Newtown, Connecticut, in December 2012.

The tragedy was the latest in a seemingly unending string of mass killings at churches, schools, stores and other sites in the U.S. Just 10 days earlier, 10 Black people were shot to death in a racist rampage at a Buffalo, New York, supermarket.

In a somber address to the nation hours after the attack in Texas, President Joe Biden pleaded for Americans to “stand up to the gun lobby” and enact tougher restrictions, saying: “When in God’s name are we going to do what has to be done?”