On May 28, investigators in Uvalde, Texas, sought to determine how critical errors were made in response to the deadly school shooting there last Thursday, including why nearly 20 officers remained outside a classroom while children dialed 911 for assistance.

The officers’ decision to wait nearly an hour in the hallway before entering and fatally shooting the gunman is central to the Texas Department of Public Safety investigation into the murder of 19 youths and two teachers in the United States’ deadliest school shooting in nearly a decade.

Law enforcement from across Texas have arrived in Uvalde to assist local authorities, KSAT reports.

According to Colonel Steven McCraw, director of the Texas Department of Public Safety, at least two children called 911 from a pair of adjoining fourth-grade classrooms after Ramos entered on Tuesday with a semi-automatic rifle.

Children inside the school placed at least eight calls to emergency services while law enforcement waited outside. According to McCraw, how many of the 9- and 10-year-old schoolchildren may have been killed during that time remains unclear. The two children who placed the calls survived.

McCraw said that the on-site commander and the chief of the school district’s police department mistakenly determined that Ramos was barricaded inside and that children were no longer at risk, giving officers time to prepare for an assault.

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“With the benefit of hindsight, where I’m sitting now, of course it was not the right decision, it was a wrong decision, period,” he said. “There’s no excuse for that, but again, I wasn’t there.”

McCraw said that, from what law enforcement now knows, they should have entered the school.

“When there’s an active shooter, the rules change,” McCraw said, acknowledging that standard protocols call for police to immediately confront an active school shooter rather than wait for backup.

Border Patrol tactical agents at the scene were frustrated with a lack of clear direction from the commander, believing it delayed efforts to end the attack, said a law-enforcement source familiar with the matter.

When the Border Patrol agents entered the classroom behind a ballistic shield, the shooter emerged from a closet, firing at them, the source said. Ramos was shot and killed.

The official accounts of how police responded to the shooting flip-flopped wildly. The day after the killings, Texas Governor Greg Abbott praised the courage of the police, who he said had saved lives.

On Friday, during a press conference, he said he was “livid” and had been misled by investigators about the response and that it was “imperative” that investigators answer 100% of the questions that remain about the shooting.

U.S. Representative Joaquin Castro of Texas has called for an independent FBI investigation into the police response. He visited the school on Saturday and told reporters he was deeply disturbed about the emerging conflicting information.

Despite the fact that at least two state Department of Public Safety officers were among the 19 officers who waited outside the classroom, both the DPS director and the state’s governor have stated that they were misled, according to Castro.

“I don’t understand who exactly lied to them about what happened,” Castro said. “State authorities are trying to blame locals for everything that happened. But right now it’s not just adding up.”

USA Today reports Javier Cazares, whose daughter, Jacklyn, 9, died in the hospital after being shot inside the school, is distraught over the possibility that she died because of the long wait for help. He wants to know what went wrong with the police response and holds those responsible accountable.

As reported by Reuters, Cazares said, “My little girl was shot, and who knows how long she was bleeding on the floor of her classroom? God knows how long she was gasping for her little life.”