The massacre of 19 children and two teachers in a Texas elementary school this week started and continued amid numerous instances of mistakes, misjudgments or misfortune, according to newly released details.

A Texas official on Friday laid out the clearest picture yet of what authorities believe happened before, during and immediately after the deadly rampage. Steven McCraw, director of the Texas Department of Public Safety, spoke to a crowd of reporters frustrated by the changing narrative of what happened Tuesday morning.

He detailed numerous points where the shooter could have been stopped — but the massacre continued for various reasons.

“Ultimately, this is tragic,” McCraw said. “What do you tell the 19, the families of 19 kids, or the families of two teachers?”

Officer ‘drove right by the suspect’

There was not a school resource officer at the school when the shooter arrived Tuesday, McCraw said. Uvalde has a part-time SWAT team, and the Uvalde Consolidated Independent School District has six officers, McCraw said.

An officer who responded to the scene heard about a 911 call of a man with a gun and “drove immediately” to the school, McCraw said. The officer “sped to what he thought was the man with the gun” near the back of the school, but it “turned out to be a teacher,” McCraw said.

“In doing so, he drove right by the suspect,” who was hunkered down behind a vehicle, where he began shooting at the school, McCraw said. The gunman initially fired shots starting at 11:31 into at least three classrooms as he walked along the outside of the building, McCraw said.

Door left open, allowing gunman to enter school

The gunman entered the school through an open door two minutes later, at 11:33, McCraw said.

“That back door was propped open. It wasn’t supposed to be propped open. It was supposed to be locked, and certainly the teacher that went back for her cellphone, they propped it open again. So that was an access point that the subject used,” McCraw said.