"Critical failures" delayed the police response to the 2022 shooting in Texas that killed 19 children and two teachers, according to a damning US Department of Justice review.
The report found shortcomings in "leadership, decision-making, tactics, policy and training" led to a confused response to gunman Salvador Ramos at Robb Elementary School in Uvalde on 24 May.
Officers should have immediately broken into the classroom to confront the 18-year-old gunman - but instead they treated him like a "barricaded subject" and left him inside with 33 pupils for 77 minutes.
"The resulting delay provided an opportunity for the active shooter to have additional time to reassess and reengage his deadly actions inside the classroom," the report added.
"It also contributed to a delay in medical interventions with the potential to impact survivability."
There were at least 10 "stimulus events" over the course of an hour that could have driven police to take steps under active shooter protocols to "immediately stop the killing".
These events included "at least six separate instances of gunfire" and about "45 rounds in law enforcement officer presence".
In the 20 months since the review was announced, footage emerged of the gunman entering the school and police later waiting outside the fourth-grade (Year 5) classrooms where he opened fire.
In the aftermath of the shooting, authorities also gave wrong information to parents about whether their children had survived or not, according to the review.
'None of us is safe'
Kimberly Rubio, whose daughter was killed in the shooting, told reporters she "hopes the failures end today" and called for "criminal prosecutions" and to "enact civil gun laws".
"It [the shooting] began the day an 18-year-old was allowed to purchase an AR-15 [rifle]," she said.
"None of us are safe because these weapons are on the streets."
Another said he hopes the report "lights a fire under the district attorney".
He added: "It's hard enough waking up every day and continuing to walk on these streets… and see a cop that was standing there while our babies were murdered and bleeding out."
Velma Lisa Duran, whose sister Irma Garcia was one of the teachers killed, said she is grateful for the review but disappointed local prosecutors are yet to bring charges.
"A report doesn't matter when there are no consequences for actions that are so vile," she said.
"What do you want us to do with another report? Bring it to court."
'They deserved better'
The US attorney general, Merrick Garland, said victims and survivors of the shooting - which also injured 17 people - "deserved better".
"As a consequence of failed leadership, training, and policies, 33 students and three of their teachers - many of whom had been shot - were trapped in a room with an active shooter for over an hour as law enforcement officials remained outside," he said.
Speaking to reporters, he referred to delays in responding to the 1999 Columbine High School massacre and added: "It is now widely understood by law enforcement agencies across the country that in active shooter incidents, time is not on the side of law enforcement.
"Every second counts. And the priority of law enforcement must be to immediately enter the room and stop the shooter with whatever weapons and tools officers have with them."
The police response came under intense criticism at the time, with reports officers waited in a corridor for more than an hour while the gunman was in a classroom and pupils made panicked 911 calls.
This delay was also caused by officers looking for a key to the classroom door, according to Steven McCraw, director of the Texas Department of Public Safety.
He said in 2022 the door was not locked and there is no evidence officers even checked.
A US Border Patrol-led tactical team ultimately burst into the classroom and killed the gunman.
Describing an "atmosphere of chaos" at the scene in a July 2022 report, Texas lawmakers concluded officers "failed to prioritise saving the lives of innocent victims over their own safety".
Additionally, the latest review states Uvalde police officers had received improper active shooter training in the months leading up to the attack.
They were wrongly taught an "active shooter event" can easily morph into a "hostage crisis", the report states.
Among the many errors outlined was the failure of then chief of the Uvalde Consolidated Independent School District Police Department, Pete Arredondo, to immediately take charge.
He was the "de facto" commander, but threw his radio aside while running to the scene and did not request another.
Miscommunications stretched to the hospital where victims were initially treated, while some families were notified of deaths by people not trained to deliver that kind of devastating news.
At least five officers have lost their jobs, including Mr Arredondo.