The Uvalde school district has fired police chief Pete Arredondo, under mounting pressure in the grieving Texas town to punish officers over letting a gunman at Robb Elementary School remain in a fourth-grade classroom for more than an hour with an AR-15 style rifle as 19 children and two teachers were killed.

In a unanimous vote, the Uvalde Consolidated Independent School District's board of trustees fired Arredondo in an auditorium of parents and survivors of the May 24 massacre, making him the first officer to lose his job after one of the deadliest classroom shootings in US history.

His ouster came three months to the day after the tragedy, and less than two weeks before students return to school in Uvalde, where some children remain too scared or scarred to go back inside a classroom.

Parents, students and families arrive for a meeting of the Board of Trustees of Uvalde Consolidated Independent School District for a termination hearing. Photo / AP

Cheers from the crowd followed the vote, and some parents walked out of an auditorium in tears. Outside, several Uvalde residents called for other officers to follow Arredondo out the door.

"Coward!" some in the audience yelled as the meeting got under way.

Arredondo, who has been on leave from the district since June 22, has come under the most intense scrutiny of the nearly 400 officers who rushed to school but waited more than 70 minutes to confront the 18-year-old gunman in a fourth-grade classroom.

Most notably, Arredondo was criticised for not ordering officers to act sooner. Colonel Steve McCraw, director of the Texas Department of Public Safety, has said Arredondo was in charge of the law enforcement response to the attack.

Arredondo was not in attendance with his career on the line.

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Instead, minutes before the meeting of the Uvalde school board got under way, Arredondo's attorney released a scathing 4500-word letter that amounted to the police chief's fullest defence to date of his actions. Over 17 defiant pages, Arredondo is not a fumbling school police chief who a damning state investigation blamed for not taking command and wasted time by looking for keys to a likely unlocked door, but a brave officer whose level-headed decisions saved the lives of other students.

It alleges that Arredondo warned the district about a variety of security issues in the schools a year before the shooting and asserted he wasn't in charge of the scene. The letter also accused Uvalde school officials of putting his safety at risk by not letting him carry a weapon to the school board meeting if he were to attend, citing "legitimate risks of harm to the public and to Chief Arredondo".

"Chief Arredondo is a leader and a courageous officer who with all of the other law enforcement officers who responded to the scene, should be celebrated for the lives saved, instead of vilified for those they couldn't reach in time," George Hyde wrote.

Uvalde School Police Chief Pete Arredondo. Photo / AP

Hyde's office did not immediately return a request for comment after the vote.

Uvalde school officials have been under mounting pressure from victims' families and members of the community, many of whom have called for Arredondo's termination. Superintendent Hal Harrell had moved to fire Arredondo in July but postponed the decision at the request of the police chief's attorney.

Among those at the meeting was Ruben Torres, father of Chloe Torres, who survived the shooting in room 112 of the school. He said that as a former Marine, he took an oath that he faithfully executed willingly, and did not understand why officers did not take action when leadership failed.

"Right now, being young, she is having a hard time handling this horrific event," Torres said.

Shirley Zamora, the mother of a student at Robb Elementary, said accountability shouldn't end with Arredondo's dismissal.

"This is just going to be the beginning. It's a long process," she said.

Only one other officer — Uvalde Police Department Lieutenant Mariano Pargas, who was the city's acting police chief on the day of the massacre — is known to have been placed on leave for his actions during the shooting.

The Texas Department of Public Safety, which had more than 90 state troopers at the scene, has also launched an internal investigation into the response by state police. State Senator Roland Gutierrez, a Democrat who represents Uvalde, said McCraw, the state police chief, also deserves scrutiny.

"You fail at something so badly that people are getting hurt, then certainly we have to have some greater accountability," he said. "And accountability means losing your job, so be it."

School officials have said the campus at Robb Elementary will no longer be used when students return on September 6. Instead, campuses elsewhere in Uvalde will serve as temporary classrooms for primary school students, not all of whom are willing to return to school after the shooting.

School officials say a virtual academy will be offered for students. The district has not said how many students will attend virtually, but a new state law passed last year in Texas after the pandemic limits the number of eligible students receiving remote instruction to "10 per cent of all enrolled students within a given school system".

Schools can seek a waiver to exceed the limit but Uvalde has not done so, according to the Texas Education Agency.

New measures to improve school safety in Uvalde include "8-foot, non-scalable perimeter fencing" at elementary, middle and high school campuses, according to the school district. Officials say they have also installed more security cameras, upgraded locks, enhanced training for district staff and improving communication.