The alleged gunman had close to 500 rounds of ammunition when he entered the Georgia elementary school. On Wednesday, a portrait emerged of the school's front office worker who dialed 911 and calmly spoke to the gunman, persuading him to surrender. NBC's Kate Snow reports.

The troubled young man who allegedly walked into a Georgia elementary school with a high-powered rifle and hundreds of rounds of ammo told a staffer that he didn't care about dying and should have just gone to a mental hospital, 911 tapes revealed Wednesday.

Michael Brandon Hill, 20, is charged with aggravated assault on a police officer, making terroristic threats and possession of a firearm by a convicted felon after he fired at least six shots in the front office of Ronald E. McNair Discovery Learning Academy near Atlanta. Police returned fire, yet no one was hurt.

But Hill's first stop was at the school's front desk, where a school bookkeeper, Antoinette Tuff, called 911 and then, for almost 25 minutes, stayed on the line, relaying what Hill was doing and saying, according to the tape released Wednesday.

Tuff told the 911 operator that Hill said he "should have just went to the mental hospital instead of doing this because he is not on his medication" — the same thing he later told investigators, authorities said.

"He said he don't care if he dies, he don't have nothing to live for," Tuff told the operator. "He said he's not mentally stable."

Occasionally, Hill himself can be heard speaking, at one point saying, "Tell them to stop bothering me," and a little bit later yelling, "Tell them to stand down now!"

Tuff told DeKalb County emergency dispatchers that Hill had said several other disturbing things: that he was on probation — which Georgia court records confirm — and that he'd been among the school's children before, apparently during a school field trip or concert, when he played the drums for them.

A nearby resident recorded the chaotic scene near Tuesday's school shooting in Georgia. The video captures what sounds like gunshots coming from the crime scene.

Tuff even mustered up the courage to talk Hill into surrendering — a one-on-one negotiation captured on the tape.

"Don't feel bad, baby," she can be heard telling the young man. "My husband just left me after 33 years. ... I've got a son that's multiple disabled."

Later, she can be heard reassuring him that "it's all going to be well."

After about 20 minutes, she won him over.

Tuff: "OK, he said that they can come in now. He needs to go to the hospital."

Operator: "OK, and he doesn't have any weapons on him or anything like that?"

DeKalb County police Det. Ray Davis says the Georgia elementary school shooting suspect had "500 rounds of ammo with him."

Tuff: "He's laying on the floor. He's got everything out of his pockets. There isn't anything. The only thing he has is his belt. Everything is out of his pockets. Everything is sitting here on the counter, so all we need to do is they can just come in, and I'll buzz them in."

Only after the ordeal was over did Tuff reveal just how scared she'd been the whole time:

"I'm going to tell you something baby — I've never been so scared in all the days in my life," she told the unidentified operator. Then, she started crying and exclaimed, "Oh, Jesus! Oh, God!"

To which the operator told the courageous bookkeeper: "You did great. Hold on. Hold on"

Meanwhile, DeKalb County police Det. Ray Davis, the lead investigator on the case, said Wednesday that authorities are trying to find the owner of the rifle Hill used, which he said they believe Hill got from an acquaintance's house.

A photo of Hill holding a rifle, believed to be the same one, was found on Hill's cellphone, Davis said. It was a .762-caliber AK-47-style weapon, manufactured by Romarm/Cugar.

Hill pleaded guilty in July in Henry County, south of Atlanta, to making terroristic threats. Court records show that he was sentenced to three years' probation and anger counseling. Because that charge is a felony in Georgia, Hill would have been barred from possessing a weapon.

Hill's brother, Timothy, told NBC News that the charge stemmed from Hill's threatening to shoot him. He agreed that there was no way his brother could have legally bought the weapon through a licensed firearms dealer.

"He had to get them from buying them off the streets," Timothy Hill said. "There is no way possible a gun store would sell them to him with his mental history. And no gun laws would have prevented that."

Elizabeth Chuck, Tom Winter and Erika Angulo of NBC News contributed to this report.

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