UVALDE, Texas - 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 semiautomatic 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 the gunman, 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, the gunman sent the first of three messages online, Gov. Abbott said. He 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 Gov. Abbott. Investigators said the shooter did not specify which school.

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 of 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, fight- ing 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 Gov. Abbott for governor, interrupted Wednesday’s news conference, calling the tragedy “predictable.” Pointing his finger at the governor, he said: “This is on you until you choose to do something different. This will continue to happen.” Mr. 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,” Lt. 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 the gunman 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, Conn., 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, N.Y., supermarket.

In a somber address to the nation hours after the attack in Texas, President 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?”

But the prospects for any reform of the nation’s gun regula- tions appeared dim. Repeated attempts over the years to expand background checks and enact other curbs have run into Republican opposition in Congress.

The shooting came days before the National Rifle Associa- tion annual convention was set to begin in Houston, with the Texas governor and both of the state’s Republican U.S. senators scheduled to speak.

On social media in the days and hours before the massacre, the shooter appeared to drop hints that something was going to happen.

On the day he bought his second weapon last week, an Instagram account that investigators say apparently belonged to him carried a photo of two AR-15-style rifles. That post tagged another Instagram user, one with more than 10,000 followers, asking her to share the picture.

“I barely know you and u tag me in a picture with some guns,” replied the Instagram user, who has since removed her profile. “It’s just scary.”

On the morning of the attack, the account linked to the gunman replied: “I’m about to.”

Instagram confirmed to The Associated Press that it is working with law enforcement to review the account but declined to answer questions about the postings.

Investigators also are looking at an account on TikTok, possibly belonging to the shooter, with a profile that reads: “Kids be scared IRL,” which stands for “in real life.”

Investigators do not yet know why the gunman targeted the school, said Steve McCraw, director of the Department of Public Safety.

“We don’t see a motive or catalyst right now,” he said.

Officers found one of the rifles in the gunman’s truck, the other in the school, according to the briefing given to lawmakers. He was wearing a tactical vest, but it had no hardened body-armor plates inside, lawmakers were told. He also dropped a backpack containing several magazines full of ammunition near the school entrance.

One of the guns was purchased at a federally licensed dealer in the Uvalde area on May 17, according to state Sen. John Whitmire, who was briefed by investigators. He bought 375 rounds of ammunition the next day, then purchased the second rifle last Friday.

On Tuesday morning, the gunman shot and wounded his grandmother at her home, then left. Neighbors called police when she staggered outside and they saw she had been shot in the face, Department of Public Safety spokesperson Travis Considine said.

He then crashed his truck through a railing on the school grounds, and an Uvalde school district officer exchanged fire with him and was wounded, Mr. Considine said. He went inside and traded more gunfire with two arriving Uvalde police officers, who were still outside, Mr. Considine said. Those officers were also wounded.

Dillon Silva, whose nephew was in a classroom, said students were watching the Disney movie “Moana” when they heard several loud pops and a bullet shattered a window. Moments later, their teacher saw the attacker stride past the door.

“Oh, my God, he has a gun!” the teacher shouted twice, according to Mr. Silva. “The teacher didn’t even have time to lock the door,” he said.

On Wednesday morning, volunteers were seen arriving at the town civic center with Bibles and therapy dogs. Three children and an adult remained at a San Antonio hospital, where two of them — a 66-year-old woman and 10-year-old girl — were listed in serious condition.

Uvalde is about 75 miles from the Mexican border. Robb Elementary, which has nearly 600 students in second, third and fourth grades, is a single-story brick structure in a mostly residential neighborhood of modest homes.

The close-knit community, built around a shaded central square, includes many Hispanic families who have lived there for generations. It sits amid fields of cabbage, onions, carrots and other vegetables. But many of the steadiest jobs are supplied by companies that produce construction materials.

The attack came as Robb Elementary was counting down to the last days of the school year with a series of themed days. Tuesday was “Footloose and Fancy,” with students wearing nice outfits.

Eugene Garcia, Dario Lopez-Mills and Elliot Spagat in Uvalde, Jake Bleiberg in Dallas, Ben Fox, Michael Balsamo, Amanda Seitz and Eric Tucker in Washington, Paul J. Weber in Austin, Juan Lozano in Houston, Gene Johnson in Seattle and Rhonda Shafner in New York contributed to this report.