The 18-year-old gunman who slaughtered 19 children and two teachers at a Texas elementary school barricaded himself inside a single classroom and “began shooting anyone that was in his way,” authorities said Wednesday in detailing the latest mass killing to rock the U.S.

Law enforcement officers eventually broke into the classroom and killed the gunman, who used an AR-style rifle. Police and others responding to Tuesday’s attack also went around breaking windows at the school to enable students and teachers to escape, Lt. Christopher Olivarez of the Texas Department of Public Safety said on NBC’s “Today” show.

Olivarez told CNN that all the victims were in the same fourth-grade classroom at Robb Elementary.

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

Dillon Silva, whose nephew was in a nearby classroom, said students were watching a movie when a bullet shattered a window. Moments later, their teacher saw the armed assailant walk past the door.

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

Investigators did not immediately disclose a motive but identified the assailant as Salvador Ramos, a resident of the community about 85 miles (135 kilometers) west of San Antonio.

Ramos had hinted on social media that an attack could be coming, suggesting that “kids should watch out,” according to state Sen. Roland Gutierrez, who said he had been briefed by state police.

Ramos legally brought two AR-style rifles just days before the attack, soon after his 18th birthday, state senators briefed by law enforcement said.

One of the guns was purchased at a federally licensed dealer in the Uvalde area on May 17, according to Sen. John Whitmire. Ramos bought 375 rounds of ammunition the next day, then purchased the second rifle on May 20.

On that day, an Instagram account appearing to belong to the gunman shared a photo of two AR-style rifles.

Officers found one of the rifles in Ramos’ truck, the other in the school, according to the briefing. Ramos 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.

The attack in the heavily Latino town of Uvalde 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.

Families in Uvalde waited hours for word on their children. At the town civic center where some gathered Tuesday night, the silence was broken repeatedly by screams and wails. “No! Please, no!” one man yelled as he embraced another man.

“My heart is broken today,” said Hal Harrell, school district superintendent. “We’re a small community, and we’re going to need your prayers to get through this.”

Adolfo Cruz, a 69-year-old air conditioning repairman, was still outside the school as the sun set, seeking word on his 10-year-old great-granddaughter, Eliajha Cruz Torres.

He drove to the scene after receiving a terrifying call from his daughter about the first reports of the shooting. Waiting, he said, was the heaviest moment of his life.

“I hope she is alive,” Cruz said.

On Wednesday morning, volunteers were seen arriving at the community center with Bibles and therapy dogs.

The attack was the latest in a seemingly unending string of mass killings at churches, schools, stores and other sites in the United States. 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 bloodshed in Uvalde, President Joe Biden pleaded for new gun restrictions.

“As a nation we have to ask: When in God’s name are we going to stand up to the gun lobby? When in God’s name are we going to do what has to be done?” he asked. “Why are we willing to live with this carnage?”

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

Before the attack, Ramos shot and wounded his grandmother, then fled the scene, crashing his truck near the school and entering the building, authorities said. Inside the barricaded classroom, he “just began shooting anyone that was in his way,” Olivarez said.

A tactical team forced its way into the classroom and was met with gunfire from Ramos but shot and killed him, according to Olivarez.

Earlier, a law enforcement official said one Border Patrol agent who was working nearby when the shooting began rushed into the school without waiting for backup and shot and killed the gunman. The official spoke on condition of anonymity because he was not authorized to talk about it.

The agent was wounded but able to walk out of the school, the law enforcement official said.

Jason Owens, a top regional official with the Border Patrol, said some area agents have children at Robb Elementary.

“It hit home for everybody,” he said.

Staff members in scrubs and devastated victims’ relatives could be seen weeping as they walked out of Uvalde Memorial Hospital, which many of the children were taken. Three children and an adult were being treated at a San Antonio hospital, where two of them — a 66-year-old woman and 10-year-old girl — were reported in serious condition.

Uvalde, home to about 16,000 people, is about 75 miles (120 kilometers) from Mexican borer. 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 attack came as the school was counting down to the last days of the school year with a series of themed days. Tuesday was to be “Footloose and Fancy,” with students wearing nice outfits.

Law enforcement officers investigating the bloodshed began serving search warrants and gathering telephone and other records. They also sought to contact Ramos’ relatives and trace the guns.

Condolences poured in from leaders around the world. Pope Francis pleaded that it was time say “‘enough’ to the indiscriminate trade of weapons!” Ukrainian Foreign Minister Dmytro Kuleba said his nation also knows “the pain of losing innocent young lives.”

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

In 2018, a gunman killed 10 people at Santa Fe High School in the Houston area. A year before that, a gunman shot more than two dozen people to death during a Sunday service in the small town of Sutherland Springs. In 2019, a gunman at a Walmart in El Paso killed 23 people in a racist attack targeting Hispanics.

The shooting came days before the National Rifle Association annual convention was set to begin in Houston. Gov. Greg. Abbott and both of Texas’ U.S. senators, all of them Republicans, were among the scheduled speakers at a forum Friday.