Investigators in Texas on Saturday sought to determine how critical mistakes were made in the response to the deadly Uvalde school shooting, including why nearly 20 officers remained outside a classroom as children placed panicked 911 calls for help.
Why the officers waited in the hallway nearly an hour before entering and fatally shooting the gunman is at the heart of a probe by the Texas Department of Public Safety into the massacre of 19 children and two teachers in the deadliest US school shooting in nearly a decade.
With calls mounting for an independent probe and criticism of the law-enforcement response growing, police from cities as far away as Houston and Dallas have arrived in Uvalde to help support local authorities, in some cases providing protection to Uvalde's own police, the mayor, and the gun shop where the shooter bought two semi-automatic rifles.
Meanwhile, investigators are still searching for a motive. Salvador Ramos, an 18-year-old high school dropout, had no criminal record and no history of mental illness, although threatening messages he sent on social media are coming to light.
At least two children placed 911 calls from a pair of adjoining fourth-grade classrooms after Ramos entered on Tuesday with an AR-15 semi-automatic rifle, Colonel Steven McCraw, director of the Texas Department of Public Safety, said earlier this week.
"He's in room 112," a girl whispered on the phone at 12:03 pm. The same girl had implored a 911 operator to "please send the police now" at 12:43 pm and again four minutes later. At 12:51, or more than 45 minutes after she made her first 911 call, a US Border Patrol-led tactical team stormed in and ended the siege at the Robb Elementary School.
In all, at least eight calls to emergency services were placed from inside while law enforcement waited outside.
It remains unclear how many of the 9- and 10-year-old schoolchildren may have been killed during that time. The two children who placed calls survived.
The on-site commander, the chief of the school district's police department, mistakenly determined that Ramos was barricaded inside and that children were no longer at risk, giving officers time to prepare for an assault, McCraw said.
"It was the wrong decision, period," McCraw said, acknowledging that standard protocols call for police to confront an active school shooter immediately, rather than wait for backup.