(Reuters) – Uvalde police officers waited more than an hour before storming into two elementary school classrooms, where a gunman had been holed up. Supervisors on the scene knew some of those victims were still alive, according to The New York Times.

The Times cited video footage from investigators and said that more than 12 of 33 children and 3 teachers were in those classrooms when gunfire started. This was between the time officers arrived and shot the suspect.

According to video and other evidence, the school district chief of police who led the response seemed to be pondering over the time it took to get protective gear for officers when they charged in and how to unlock the doors to his classroom, according to The Times.

A transcript from police body-camera footage shows that Pete Arredondo was the chief of Uvalde Consolidated Independent Schools District’s police force. “We are trying to preserve the remaining days of our lives.”

Robb Elementary School, Uvalde in Texas Hill Country, was attacked on May 24, killing 19 students and 2 teachers. It is the most deadly school shooting incident in nearly a decade.

The Times cites documents that show one teacher died in an ambulance while three children were killed at local hospitals. This raises questions as to whether additional lives might have been saved if the victims had been reached earlier.

Texas Department of Public Safety (DPS), days later, publicly acknowledged that up to 19 officers waited approximately an hour in a corridor outside of classes 111 and 112 until a U.S. Border Patrol-led tactical unit finally entered.

DPS officials claim that Arredondo decided to delay sending in officers to neutralize him, as he believed the immediate threat to the students in his classrooms had subsided after the initial gunfire.

The bullets that were fired at two officers as they attempted to approach one of the classrooms grazed them. Police say no other attempt was made for 40 minutes.

Steven McGraw (head of DPS) said that the delay was “the wrong choice.” He also acknowledged that at least two fourth grade girls, who were hiding in the classrooms, made frantic phone calls to 911 dispatchers, begging for help.

According to the Times, it is not clear if Arredondo or any other school officers were aware of the 911 calls.

The newspaper said that Arredondo, along with others on the scene, became aware that not all of the students in the classrooms were dead at one point.

Ruben Ruiz was one of six uniformed school police officers in Arredondo’s district force. Mireles died later from her injuries.

The Times stated that Arredondo didn’t respond to multiple requests for comment.