Frantic children called 911 more than half a dozen times from the Texas classrooms where a massacre was unfolding, pleading for police to intervene, as some 20 officers waited in the hallway nearly an hour before entering and killing the gunman.
At least two children placed several emergency calls from a pair of adjoining fourth-grade classrooms after 18-year-old Salvador Ramos entered on Tuesday with an AR-15 semi-automatic rifle, according to Colonel Steven McCraw, director of the Texas Department of Public Safety.
Ramos, who had driven to Robb Elementary School from his home after shooting and wounding his grandmother, went on to kill 19 children and two teachers in the deadliest US school shooting in nearly a decade.
"He's in room 112," a girl whispered on the phone at 12.03pm local time, more than 45 minutes before a US Border Patrol-led tactical team finally stormed in and ended the siege.
The on-site commander, the chief of the school district's police department in Uvalde, Texas, believed at the time Ramos was barricaded inside and children were no longer at immediate risk, giving police time to prepare, McCraw said.
"From the benefit of hindsight where I'm sitting now, of course it was not the right decision," McCraw said. "It was the wrong decision, period."
The disclosure of local law enforcement's delay in pursuing the teenaged gunman came as the nation's leading gun-rights advocacy group, the National Rifle Association, opened its annual convention 450 kilometres away in Houston.
Governor Gregg Abbott, a Republican and staunch gun-rights proponent who addressed the meeting in a pre-recorded video, seized on apparent police lapses in Uvalde, telling a news conference later he was misled and "livid about what happened".
Abbott denied newly enacted Texas gun laws, including a controversial measure removing licensing requirements for carrying a concealed weapon, had "any relevancy" to Tuesday's bloodshed.
He suggested state lawmakers focus renewed attention on addressing mental illness.
The latest chronology of the Uvalde school attack stirred dismay, including among the officials reporting it.
McGraw, whose voice choked with emotion at times, said, "We're here to report the facts, not to defend what was done or the actions taken."
Some of the mostly nine- and 10-year-old students trapped with the gunman survived the massacre, including at least two who called 911, McCraw said.
There were at least eight calls to 911 between 12.03pm, half-an-hour after Ramos entered the building, and 12.50pm, when Border Patrol agents and police burst in and shot the gunman dead.
A girl called at 12.16pm and told police there were still "eight to nine" students alive, the colonel said. Three shots were heard during a call made at 12.21pm.
The girl who made the first call implored the operator to "please send the police now" at 12.43pm and again four minutes later.
Officers went in three minutes after that final call, according to McCraw, when the tactical team used a janitor's key to open the locked classroom door.
There were as many as 19 officers in the hallway by 12.03pm, when the first 911 call from inside the classroom was received, McCraw said.
Standard law enforcement protocols call for police to confront an active school shooter without delay, rather than waiting for backup or more firepower, a point McCraw acknowledged on Friday.
Medical experts also stress the importance of evacuating critically wounded gunshot patients to a trauma centre within 60 minutes - what emergency physicians call "the golden hour" - in order to save lives.
The attack came 10 days after a shooting in Buffalo, New York that left 10 people dead.
At the NRA meeting, prominent Republicans including former president Donald Trump and US Senator Ted Cruz of Texas, doubled-down on arguments tighter gun laws would do little or nothing to allay the rising frequency of mass shootings.
About 500 protesters holding crosses, signs and photos of victims from the Uvalde shooting gathered outside the convention.
President Joe Biden, who has urged Congress to approve new gun restrictions, will on Sunday visit the community of 16,000 people about 130km west of San Antonio.
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