School bookkeeper Antoinette Tuff is being hailed as a hero after she averted what could have been a catastrophic elementary school shooting in an Atlanta suburb.

On Tuesday, Michael Brandon Hill, 20, slipped past school security at the Ronald E. McNair Discovery Learning Academy, a school for pre-kindergarteners to fifth graders. He was armed with an assault rifle and other weapons.

The outcome could have been tragic, but thanks to Antoinette Tuff’s quick thinking, Hill never got past the front office. Even as Hill held her and an officemate hostage, she said she spoke to him calmly and ultimately convinced him to lay down his weapons.

“He had a look on him that he was willing to kill,” she said in an interview with ABC’s World News with Diane Sawyer. “He said that he didn’t have any reason to live and that he knew he was going to die today…I knew that if he got out that door he was gonna kill everybody.”

Watch Tuff’s account of the harrowing incident:

https://www.youtube.com/watch?v=MelQCClmDD8

At one point, Hill asked Tuff to call 911, and she stayed on the line for nearly 25 minutes with the dispatcher, relaying what Hill was doing and saying.

In the 911 tapes released Wednesday and excerpted by NBC News, Tuff can be heard trying to calm Hill down by telling him about her own life struggles.

“Don’t feel bad, baby,” she said. “My husband just left me after 33 years…I’ve got a son that’s multiple disabled.” She added, “It’s all going to be well.”

She told the 911 operator, “He said he don’t care if he dies, he don’t have nothing to live for. He said he’s not mentally stable.”

Later, Hill could be heard saying, “Tell them to stop bothering me,” and yelling, “Tell them to stand down now!”

Tuff also told the 911 dispatcher that Hill said he was on probation, and that he had spent time with children at the school in the past, during a school field trip or concert.

As this tense situation played out in the front office, students and teachers fled the building and waited in a field until school buses arrived to take them to a nearby Wal-Mart, where their families were waiting.

Tuff continued to talk calmly to the shooter, and says she asked him to put his weapons and backpack on the floor.

Hill reportedly exchanged fire with officers before being arrested. No students, teachers, or police officers were injured during the incident.

“It’s a blessed day, all of our children are safe,” said DeKalb County Schools Superintendent Michael Thurmond at a news conference. “This was a highly professional response on the ground by DeKalb County Employees assisted by law enforcement.”

On Wednesday, authorities revealed Hill had been carrying 500 rounds of ammunition. He was charged with aggravated assault on a police officer, terroristic threats, and possession of a firearm by a convicted felon. His motive was unclear, though apparently he has made violent threats in the past.

According to police, he sent his brother Timothy a Facebook message last December saying “that he would shoot him in the head and not think twice about it.” Timothy Hill told police at the time that his brother had a “long history of medical disorders.”