Houston (AFP) - A damning Justice Department report on Thursday cited "critical failures" by Texas law enforcement who waited until 21 people had been killed by a mass shooter at a school before finally intervening.

Nineteen young children and two teachers were killed when a teenage gunman went on a rampage at Uvalde's Robb Elementary School in May 2022 in America's worst school shooting in a decade. Police eventually shot and killed the attacker.

Investigators "identified several critical failures," the report said, and "the most significant failure was that the responding officers should have immediately recognized the incident as an active shooter situation."

"In summary, the response to the May 24, 2022, mass casualty incident at Robb Elementary School was a failure," said the critical incident review which is more than 550 pages long. "The painful lessons detailed in this report are not meant to exacerbate an already tragic situation."

Police in Uvalde as well as local political leadership have been under intense scrutiny since it emerged that more than a dozen officers waited for over an hour outside classrooms where the shooting was taking place and did nothing as children lay dead or dying inside.

"This community deserved more than misinformation from officials during and after the attack," US Attorney General Merrick Garland said at a Thursday news conference in the small Texas town.

"Within minutes of arriving inside the school, officials on scene transitioned from treating the scene as an active shooter situation to treating the shooter as a barricaded subject," he added. "This was the most significant failure." 

'Chaotic'

A total of 376 officers -- border guards, state police, city police, local sheriff departments and elite forces -- responded to the massacre, a Texas state lawmakers' report said in July 2022.

But the situation was "chaotic" due to the officers' "lackadaisical approach" to subduing the gunman, the report charged.

"The shooter was not killed until approximately 77 minutes after law enforcement first arrived," it said.

In October 2022, the Uvalde Consolidated Independent School District said it was suspending the small police force that has responsibility for safety and security in the handful of public schools under its authority.

Kimberly Mata-Rubio, whose 10-year-old daughter was killed, called for government accountability.

"I hope that the failures end today and that local officials do what wasn't done that day, do right by the victims and survivors of Robb Elementary: terminations, criminal prosecutions," she said at the news conference.

Adrian Alonzo, the uncle of slain 9-year-old Eliahna "Ellie" Garcia, told AFP the new report did not add to what victims' families already knew.

"I was expecting some kind of accountability," he said. "Maybe it's too early to tell if there will be any criminal (charges) or terminations that come after this."

School shootings have become a regular occurrence in a country where about a third of adults own a firearm and regulations on purchasing even powerful military-style rifles are lax.

Polls show a majority of voters favor stricter controls on the use and purchase of firearms. However, the gun-ownership lobby is highly influential and courts have ruled that the constitutional right to bear arms applies to private owners.

In June 2022, reform advocates secured a limited victory with the passage of legislation that demands enhanced background checks for younger buyers and provides federal cash for states introducing "red flag" laws that allow courts to temporarily remove weapons from those considered a threat.

President Joe Biden praised the legislation in a statement Thursday while also calling for Congress to "pass common sense gun safety laws to ensure that mass shootings like this one don't happen in the first place."

Investigators compiling the Uvalde report, which intentionally did not name the shooter "to avoid glorifying the subject's actions," collected and reviewed "more than 14,100 pieces of data and documentation, including policies, training logs, body camera and CCTV video footage."