Texas investigators were trying to figure out how significant errors were made in the aftermath of the deadly Uvalde shooting, such as why nearly 20 police officers stayed outside a primary school classroom while children dialled 911 for help.

Why the officers waited nearly an hour in the hallway before entering and fatally shooting the gunman is the subject of an ongoing investigation by the Texas Department of Public Safety into the massacre of 19 children and two teachers in the deadliest school shooting in the United States in nearly a decade.

Investigators are currently looking into the attack’s motive. Salvador Ramos, a high school dropout with no criminal record or mental illness history, was arrested.

Colonel Steven McCraw, director of the Texas Department of Public Safety, said earlier this week that at least two youngsters called 911 from a pair of adjoining fourth-grade classrooms after 18-year-old Ramos entered on Tuesday with an AR-15 semi-automatic weapon.

“He’s in room 112,” a girl said on the phone at 12:03 p.m., more than 45 minutes before a tactical squad commanded by the US Border Patrol burst into the Robb Elementary School in Uvalde, a town of 16,000 people west of San Antonio, and ended the siege.

At 12:43 p.m. and four minutes later, the same girl pleaded with the 911 operator to “please send the cops now.”

According to McCraw, the on-site commander, the chief of the school district’s police department, felt at the time that Ramos was locked inside and that the children were no longer in immediate danger, allowing cops to prepare.

“From where I’m sitting now, with the benefit of hindsight, it was obviously not the proper decision,” McCraw said. “It was a bad decision all around.”