The delay in confronting the shooter - who was inside the school for more than an hour - could lead to discipline, lawsuits and even criminal charges against police.
The attack that left 19 children and two teachers dead in a fourth grade classroom was the nation's deadliest school shooting in nearly a decade, and for three days police offered a confusing and sometimes contradictory timeline that drew public anger and frustration.
By Friday, authorities acknowledged that students and teachers repeatedly begged 911 operators for help while the police chief told more than a dozen officers to wait in a hallway at Robb Elementary School. Officials said he believed that the suspect was barricaded inside adjoining classrooms and that there was no longer an active attack.
The chief's decision - and the officers' apparent willingness to follow his directives against established active-shooter protocols - prompted questions about whether more lives were lost because officers did not act faster to stop the gunman, and who should be held responsible.
"In these cases, I think the court of public opinion is far worse than any court of law or police department administrative trial," said Joe Giacalone, a retired New York police sergeant. "This has been handled so terribly on so many levels, there will be a sacrificial lamb here or there."
As the gunman fired at students, law enforcement officers from other agencies urged the school police chief to let them move in because children were in danger, two law enforcement officials said.
The officials spoke on condition of anonymity because they had not been authorized to talk publicly about the investigation.
One of the officials said audio recordings from the scene capture officers from other agencies telling the school police chief that the shooter was still active and that the priority was to stop him. But it wasn't clear why the school chief ignored their warnings.
Texas Gov. Greg Abbott, who at a news conference earlier in the week lauded the police for saving lives, said he had been misled about the initial response and promised there would be investigations into "exactly who knew what, when, who was in charge" and what they did.
"The bottom line would be: Why did they not choose the strategy that would have been best to get in there and to eliminate the killer and to rescue the children?" Abbott said.
Criminal charges are rarely pursued against law enforcement in school shootings. A notable exception was the former school resource officer accused of hiding during the 2018 shooting at Marjory Stoneman Douglas High School in Parkland, Florida, that that left 17 people dead.
Potential administrative punishments - meted out by the department itself - could range from a suspension or docked pay to forced resignation or retirement or outright termination.
In terms of civil liability, the legal doctrine called "qualified immunity," which shields police officers from lawsuits unless their actions violate clearly established laws, could also be at play in future litigation.
The Uvalde School District police chief, Pete Arredondo, decided that the group of officers should wait to confront the assailant, on the belief that the active attack was over, according to Steven McCraw, the head of the Texas Department of Public Safety.
The crisis ended shortly after officers used keys from a janitor to open the classroom door, entered the room and shot and killed Ramos.
Arredondo could not be reached for comment Friday, and Uvalde officers were stationed outside his home, but they would not say why.
Prosecutors will have to decide whether Arredondo's decision and the officers' inaction constituted a tragic mistake or criminal negligence, said Laurie Levenson, a former federal prosecutor who is a professor at Loyola Law School in Los Angeles.
Levenson said prosecutors could bring state felony charges of criminally negligent homicide, though she said federal civil rights charges would be unlikely because they require intent.
"I don't know that we expect every officer to make a perfect decision on the spot," she said. "But waiting this long - given what we know about how shooters act - predictably leads to tragedy."
In the Parkland case, former Broward County Deputy Scot Peterson is scheduled to go to trial in September on charges of child neglect resulting in great bodily harm, culpable negligence and perjury. He has said he did the best he could at the time.
The "unprecedented and irresponsible" decision by Florida prosecutors to bring a criminal case against Peterson might lead to other police elsewhere being "stripped of their liberty" and facing decades in prison "solely because a finding is made after the fact that things could have been handled differently," Mark Eiglarsh, the former deputy's attorney, said in an email.
Maria Haberfeld, a professor at John Jay College of Criminal Justice in New York, said the police department's policies, procedures and training will be scrutinized to see whether the officers on the ground in Uvalde followed them.
If they did, and criminal charges are still brought, she said it would send a chilling message to police nationwide. "If you follow your procedures, you're still brought up on charges. So what's the point of having procedures?" she said.
But Jorge Colina, a former Miami police chief, wants to know more about what was going through the minds of the officers inside the school as the chief told them to wait in the hall.
"Did someone challenge the decision there?" he said. "Did someone raise an objection at least?"
Associated Press writers Jim Vertuno in Uvalde, Texas; Jake Bleiberg in Dallas; Terry Spencer in Fort Lauderdale, Florida; and Mike Balsamo in Washington, D.C., contributed to this report.