More than a year ago, tips about online posts threatening a school shooting led Georgia police to interview a 13-year-old boy, but investigators didn't have enough evidence for an arrest.

That boy is now accused of opening fire at his high school outside Atlanta on Wednesday and killing four people and wounding nine.

The teen has been charged as an adult in the deaths of Apalachee High School students Mason Schermerhorn and Christian Angulo, both 14, and instructors Richard Aspinwall, 39, and Christina Irimie, 53, Georgia Bureau of Investigation director Chris Hosey said at a news conference.

Eight students and one teacher at the school in Winder, about an hour's drive northeast of Atlanta, were taken to hospitals with injuries. All were expected to survive, Barrow County Sheriff Jud Smith said.

The teen, now 14, was to be taken to a regional youth detention facility on Thursday.

WATCH l Apalachee High students describe frightening moments: 

2 students, 2 teachers dead in Georgia high school shooting

Two students and two teachers were killed in a shooting that left at least nine others injured at Apalachee High School in Winder, Georgia. Police say a 14-year-old suspect has been charged with murder and will be tried as an adult.

The teen had been interviewed after the FBI received anonymous tips in May 2023 about online threats to commit an unspecified school shooting, the agency said in a statement. The FBI narrowed the threats down and referred the case to the sheriff's department in Jackson County, which is adjacent to Barrow County.

The sheriff's office interviewed the then-13-year-old and his father, who said there were hunting guns in the house but the teen did not have unsupervised access to them. The teen also denied making any online threats. The sheriff's office alerted local schools for continued monitoring of the teen, but there was no probable cause for arrest or additional action, the FBI said.

Hosey said the state Division of Family and Children's Services also had previous contact with the teen and will investigate whether that has any connection to the shooting. Local news outlets reported that law enforcement on Wednesday searched the teen's family home in Bethlehem, Ga., east of the high school.

Authorities were still looking into how the teen obtained the gun used in the shooting and got it into the school, which has about 1,900 students.

'I just started shaking and crying'

Armed with an assault-style rifle, the teen turned the gun on students in a hallway at the school when classmates refused to open the door for him to return to his algebra classroom, classmate Lyela Sayarath said.

The teen earlier left the classroom, and Sayarath figured the quiet student who recently transferred was skipping school again. But he returned later and wanted back in the classroom. Some students went to open the locked door but instead backed away.

"I'm guessing they saw something, but for some reason they didn't open the door," Sayarath said. When she looked at him through a window in the door, she saw the student turn and heard a barrage of gunshots.

"It was about 10 or 15 of them at once, back to back," she said. The math students ducked onto the floor and sporadically crawled around, looking for a safe corner to hide.

Two school resource officers encountered the shooter within minutes after a report of shots fired went out, Hosey said. The teen immediately surrendered and was taken into custody.

Christopher Vasquez, 15, said he was in band practice when the lockdown order was issued.

"Once we heard banging at the door and the SWAT [team] came to take us out, that's when I knew that it was serious," he said at a Wednesday night vigil. "I just started shaking and crying."

"I just was praying that everyone I love was safe," he added.

Guns leading cause of death for U.S. kids

U.S. classroom killings have set off fervent debates about gun control and frayed the nerves of parents whose children are growing up accustomed to active shooter drills in classrooms. But they have done little to move the needle on national gun laws.

Before Wednesday, there had been 29 mass killings in the U.S. so far this year, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University. At least 127 people have died in those killings, which are defined as incidents in which four or more people die within a 24-hour period, not including the killer — the same definition used by the FBI.

While mass shootings often get significant attention in broadcast news media coverage, they account for a very small percentage of the human losses U.S. sees each year from gun violence.

A little over 48,000 people died by gunfire in 2022, according to provisional data from the Centers for Disease Control and Prevention, with just under 20,000 attributable to homicide. The majority of deaths were declared suicides, with others accidental.

But guns have been the leading cause of death for children and teens for five consecutive years, with 4,590 under the age of 19 killed in 2022.