Nearly 400 law enforcement officials rushed to the school in Uvalde, Texas, amid the mass shooting that left 21 people dead, but "systemic failures" created a chaotic scene that lasted more than an hour before the gunman was finally confronted and killed, according to a report from investigators.
The nearly 80-page report, obtained by multiple media outlets, was the first to criticise both state and federal law enforcement, and not just local authorities, for the inaction of heavily armed officers as a gunman fired inside a fourth-grade classroom.
"At Robb Elementary, law enforcement responders failed to adhere to their active shooter training, and they failed to prioritise saving innocent lives over their own safety," the report said.
According to the report, the gunman fired approximately 142 rounds inside the building and it was "almost certain" that 100 shots came before any officer entered.
The commander of a Border Patrol tactical team waited for a bullet-proof shield and working master key for the classroom, which may have not even been needed, before entering the classroom.
No-one assumed command despite scores of officers, including Pete Arredondo, the Uvalde school district police chief, being on the scene.
Mr Arredondo told the committee he treated the shooter as a "barricaded subject" and defended never treating the scene as an active-shooter situation because he did not have visual contact with the gunman.
An Uvalde Police Department officer said he heard about 911 calls that had come from inside the classroom, and his understanding was the officers on one side of the building knew there were victims trapped inside. Still, no-one tried to breach the classroom.
The report — the most complete account yet of the hesitant and haphazard response to the May 24 massacre at Robb Elementary School — was written by an investigative committee from the Texas House of Representatives and released to family members Sunday.
According to the Texas Tribune, which reviewed the report ahead of its scheduled release to the public later in the day, 376 law enforcement officers massed at the school.
The overwhelming majority of those who responded were federal and state law enforcement officers.
That included nearly 150 US Border Patrol agents and 91 state police officials, according to the Tribune.
"It's a joke. They're a joke. They've got no business wearing a badge. None of them do," Vincent Salazar, grandfather of 11-year-old victim Layla Salazer, said.
'Egregiously poor decision making'
"Other than the attacker, the committee did not find any 'villains' in the course of its investigation," the report said.
The committee did not "receive medical evidence" to show that police breaching the classroom sooner would have saved lives, but it concluded: "It is plausible that some victims could have survived if they had not had to wait 73 additional minutes for rescue."
The report followed weeks of closed-door interviews with more than 40 people, including witnesses and law enforcement officials who were on the scene of the shooting.
Flowers that had been piled high in the city's central square had been removed as of Sunday, leaving a few stuffed animals scattered around fountains alongside photos of some of the children who were killed.
A nearly 80-minute hallway surveillance video published by the Austin American-Statesman this week publicly showed for the first time a hesitant and haphazard tactical response, which the head of Texas' state police condemned as a failure and some Uvalde residents blasted as cowardly.
Calls for police accountability have grown in Uvalde since the shooting. So far, only one officer from the scene of the deadliest school shooting in Texas history is known to be on leave.
The report is the result of one of several investigations into the shooting, including another led by the Justice Department.
A report earlier this month by tactical experts at Texas State University alleged that an Uvalde police officer had a chance to stop the gunman before he went inside the school armed with an AR-15.
But in an example of the conflicting statements and disputed accounts since the shooting, Uvalde Mayor Don McLaughlin has said that never happened.
That report had been done at the request of the Texas Department of Public Safety, which Mr McLaughlin has increasingly criticised and accused of trying to minimise the role of its troopers during the massacre.
Steve McCraw, the head of Texas DPS, has called the police response an abject failure.
Paying 'with the blood of our children'
Gene Wu, a Democratic state representative in the city of Houston, Texas, told ABC NewsRadio he did not think the report was satisfactory.
"The report even says, in the very beginning, that just knowing what happened does not make this better," he said.
"What's going to make this better is by doing something about the situation."
He said the report not only laid blame on law enforcement and the school for failing to act immediately when the shooting happened, but also showed people around the shooter were aware of his intent, yet failed to take action.
"If we had a red flag law in the state, this was a situation that should have been flagged," he said.
"This person should not have been allowed to purchase a weapon."
Mr Wu is afraid that the shooting will only inspire others to take out their anger using violence.
"Americans so far have been able to sort of shield themselves from the grim reality of what this infatuation with the gun lobby has done," he said.
"The price that we've been paying [is] with the blood of our children and the blood of our loved ones.
"We can't keep being the only nation in the world where this happens on a regular basis."
AP/ABC