(CNN) — A man accused of storming into an Atlanta-area elementary school this week -- armed with an AK-47-type assault rifle and about 500 rounds of ammunition -- had been arrested months ago for threatening to kill his brother, a district attorney said Wednesday.
Michael Brandon Hill barricaded himself in the front office of the Ronald E. McNair Discovery Learning Academy in Decatur on Tuesday and fired one shot inside the school and several more at police officers outside before he eventually surrendered, DeKalb County police said.
No one was injured in the ordeal.
Yet the incident isn't the suspect's only run-in with the law. Hill, 20, had been arrested in March on a charge of "terroristic threats and acts," accused of threatening to kill his brother by Facebook in neighboring Henry County in late December, the brother said.
After pleading guilty to that charge, Hill was sentenced in July to serve three years of probation and attend anger management classes as part of a plea agreement, according to Henry County court records.
It's not clear whether Hill started the classes. Henry County District Attorney James Wright said Wednesday there is no indication that he's completed them.
Ray Davis, the DeKalb County police department's lead detective on the case, said that Hill has a "slight criminal history" in his county as well, without getting into specifics.
The suspect told investigators that he'd been "on medication and that he stopped taking it," according to Davis. Antoinette Tuff, a front office worker who told media how she calmed the gunman, said on ABC News that Hill told her he "hadn't taken his medication and that he was going to die anyway and that he was OK with dying."
Authorities are trying now to talk to family, friends and acquaintances of Hill, hoping to learn more about him and what might have spurred him to do what he did.
That includes tracking down more on the gun itself, especially since it fell into the hands of someone on probation for such a crime.
Hill himself did not own the gun, said Davis. Rather, he'd taken it from the house of an acquaintance who police are trying to talk to, in addition to the firearm's original owner.
A court appearance in the case could happen as soon as Thursday, though the detective said a day earlier that "we're not sure at this point."
The delay is partly because authorities are still working out exactly what new charges, and how many of them, Hill will face.
A police spokesman has said the counts will include aggravated assault on a police officer, making terroristic threats and possession of a firearm by a convicted felon. Davis added that, in addition to various "weapons charges," Hill should be charged with a count of false imprisonment.