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STORY: "It was the wrong decision, period."

Police in Texas on Friday admitted law enforcement's response in Uvalde fell disastrously short.

Texas Department of Public Safety Director Steve McCraw said that more than a dozen police officers waited in the hallways of Robb Elementary Tuesday, as panicked children and teachers called 911, begging for help while a gunman fired shots in their classroom.

Nineteen children would die, along with two teachers.

Outside, frantic parents were urging police to storm the school during the attack -- some even restrained by police.

The new timeline, which differed sharply from previous official accounts, fueled outrage and sparked questions about whether police should have intervened sooner.

"Texas embraces active shooter training, active shooter certification (flash) ...every officer lines up, stacks up, goes and finds where those rounds are being fired at and keeps shooting until the subject is dead, period."

But law enforcement on the scene that day elected to wait for backup, McCraw said, believing the shooter was barricaded in the classroom and no longer a threat.

Meanwhile, the calls for help began.

"I'll not say her name, but she was in room 112, called 911 at 12:03. The duration of the call was 1 minute, 23 seconds. She identified herself and whispered she's in room 112. At 12:10, she called back, 'multiple dead.'"

The unidentified caller tried again, calling at 12:13, and 12:16, saying eight or nine students were still alive. More calls followed, some from students, at 12:19, and 12:21, when three shots could be heard in the background. Another call at 12:37 and again at 12:47, when the caller asked to "please send police now."

REPORTER: "How many students died in those 48 minutes?"

MCGRAW: "I don't have that answer, we're looking into that right now."

McCraw said officers used a janitor's keys to enter the classroom at 12:50pm, nearly an hour and a half after 18-year-old Salvador Ramos entered the school with an AR-15 semi-automatic rifle and exchanged fire with officers.

In total, Ramos had 60 magazines and 1,657 rounds. He killed 21 people.

McCraw said no police officers were seriously injured.