Marisela Gamez, second from right, cries out while she is held by her husband, Mario, right, and daughter, Emily, as they gather at the memorial cross of Gamez' niece, Nevaeh Bravo, who was killed in a mass shooting at Robb Elementary School in Uvalde, Texas, on May 26, 2022. Crosses for all the victims were set up at the county courthouse. | NURI VALLBONA / REUTERS

It was 11:28 a.m. when the Ford pickup slammed into a ditch behind the low-slung Texas school and the driver jumped out carrying an AR-15-style rifle.

Twelve minutes after that, authorities say, 18-year-old Salvador Ramos was in the hallways of Robb Elementary School. Soon he entered a fourth-grade classroom. And there, he killed 19 schoolchildren and two teachers in a still-unexplained spasm of violence.

At 12:58 p.m., law enforcement radio chatter said the gunman had been killed and the siege was over.

What happened in those 90 minutes, in a working-class neighborhood near the edge of the little town of Uvalde, has fueled mounting public anger and scrutiny over law enforcement's response to Tuesday's rampage.

"They say they rushed in," said Jacinto Cazares, whose fourth-grade daughter, Jacklyn Cazares, was killed in the attack, and who raced to the school as the massacre unfolded. "We didn't see that."

On Thursday, authorities largely ignored questions about why officers had not been able to stop the shooter sooner, with Victor Escalon, regional director for the Texas Department of Public Safety, telling reporters he had "taken all those questions into consideration" and would offer updates later.

The media briefing, called by Texas safety officials to clarify the timeline of the attack, provided bits of previously unknown information. But by the time it ended, it had added to the troubling questions surrounding the attack, including about the time it took police to reach the scene and confront the gunman, and the apparent failure to lock a school door he entered.

After two days of providing often conflicting information, investigators said that a school district police officer was not inside the school when the shooter arrived, and, contrary to their previous reports, the officer had not confronted the gunman outside the building.

Many more questions than answers
Instead, they sketched out a timeline notable for unexplained delays by law enforcement.

After crashing his truck, the gunman fired on two people coming out of a nearby funeral home, Escalon said. He then entered the school "unobstructed" through an apparently unlocked door at about 11:40 a.m.

But the first police officers did not arrive on the scene until 12 minutes after the crash and did not enter the school to pursue the shooter until four minutes after that. Inside, they were driven back by gunfire from the shooter and took cover, Escalon said.

A senior federal law enforcement official tells CBS News at least two of those officers were wounded by that gunfire.

The crisis came to an end after a group of Border Patrol tactical agents entered the school roughly an hour later, at 12:45 p.m., said Texas Department of Public Safety spokesperson Travis Considine. They engaged in a shootout with the gunman, who was holed up in the fourth-grade classroom. Moments before 1 p.m., he was dead.

The senior federal law enforcement official told CBS News the gunman shot at the Border Patrol agents as soon as they reached him, wounding at least one agent. The agents then returned fire and killed the shooter.

It is the policy of U.S. Customs and Border Protection, the Border Patrol's parent agency, to put agents on administrative leave after such incidents until CBP has reviewed it.

Border Patrol Chief Raul Ortiz did not give a timeline but said repeatedly that the tactical officers from his agency who arrived at the school did not hesitate. He said they moved rapidly to enter the building, lining up in a "stack" behind an agent holding up a shield.

"What we wanted to make sure is to act quickly, act swiftly, and that's exactly what those agents did," Ortiz told Fox News.

But a law enforcement official told The Associated Press that once in the building, the agents had trouble breaching the classroom door and had to get a staff member to open the room with a key. The official spoke on condition of anonymity because he was not authorized to talk publicly about the investigation.

Department of Public Safety spokesman Lt. Christopher Olivarez told CNN that investigators were trying to establish whether the classroom was, in fact, locked or barricaded in some way.

Escalon said that during the time when the agents were confronting the shooter, the officers called for backup, negotiators and tactical teams, while evacuating students and teachers.

Ken Trump, president of the consulting firm National School Safety and Security Services, said the length of the timeline raised questions.

"Based on best practices, it's very difficult to understand why there were any types of delays, particularly when you get into reports of 40 minutes and up of going in to neutralize that shooter," he said.

Democratic Rep. Joaquin Castro, who represents the nearby San Antonio area, sent a letter to the FBI Thursday, calling on it to investigate the police response to the shooting.

Many other details of the case and the response remained murky. The motive for the massacre - the nation's deadliest school shooting since Newtown, Connecticut, almost a decade ago - remained under investigation, with authorities saying the shooter had no known criminal or mental health history.

Parents' exasperation evident
During the siege, frustrated onlookers urged police officers to charge into the school, according to witnesses.

"Go in there! Go in there!" women shouted at the officers soon after the attack began, said Juan Carranza, 24, who watched the scene from outside a house across the street.

Carranza said the officers should have entered the school sooner: "There were more of them. There was just one of him."

Cazares said that when he arrived, he saw two officers outside the school and about five others escorting students out of the building. But 15 or 20 minutes passed before the arrival of officers with shields, equipped to confront the gunman, he said.

As more parents flocked to the school, he and others pressed police to act, Cazares said. He heard about four gunshots before he and the others were ordered back to a parking lot.

"A lot of us were arguing with the police, 'You all need to go in there. You all need to do your jobs.' Their response was, 'We can't do our jobs because you guys are interfering,'" Cazares said.

As for the armed school officer, he was driving nearby but was not on campus when the gunman crashed his truck, according to a law enforcement official who was not authorized to discuss the case and spoke to the AP on condition of anonymity.

Investigators have concluded that school officer was not positioned between the school and the shooter, leaving him unable to confront the shooter before he entered the building, the law enforcement official said.

Michael Dorn, executive director of Safe Havens International, which works to make schools safer, cautioned that it's hard to get a clear understanding of the facts soon after a shooting.

"The information we have a couple of weeks after an event is usually quite different than what we get in the first day or two. And even that is usually quite inaccurate," Dorn said. For catastrophic events, "you're usually eight to 12 months out before you really have a decent picture."

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