(NewsNation) — When a Robb Elementary School staff member saw a speeding truck crash late Tuesday morning into a ditch in front of the school where she worked, her first thought was the driver had a heart attack. She called 911 to report the wreck.

She had been waiting outside the school for a co-worker to bring her supplies they were supposed to use for a school dance that was to take place the next night. She had no idea at the time that dance would never come.

The woman, a speech pathology clerk at the school, and three others began to head toward the crashed truck. That’s when she told NewsNation they saw the 18-year-old gunman had a gun and was heading toward the school. She and the others turned and fled back to the building.

In the hour after this moment, 22 lives — 19 children, two teachers and the gunman himself — would be lost.

She was still on the phone with the 911 operator when she saw the gunman reach school grounds. He had a gun around his shoulder and at least one other in a bag he threw over a fence, before hopping the fence himself. Then the shooting started.

“I told the operator, ‘He’s shooting, he’s shooting’ and all you heard is ‘pop pop pop,'” she said.

Children screamed and began running for their lives.

“There’s babies running everywhere,” she told the operator as she ran to hide under a counter in an office, asking over and over, “Where are the cops?” All she could hear were gunshots, but no sirens.

“At that point, I thought I was going to die. I (thought), ‘he’s going to come in here,'” she recounted.

From her hiding spot, she knew of the horror that was unfolding: Children were being executed.

“When I was hearing all the shots, I knew he was shooting children,” she said.

The shooting ended when an off-duty Border Patrol agent breached the classroom the gunman had locked himself in and shot and killed him.

“They were all babies. They’re innocent, even the teachers,” she said. “All of them. They had just had their awards ceremony that morning. They were happy.”