A boy accused of killing four people at his high school in Georgia was interviewed last year by police about anonymous online threats, the FBI has said.

Colt Gray, 14, denied to police in May 2023 that he was behind internet posts that contained images of guns, warning of a school shooting.

The suspect opened fire on Wednesday at Apalachee High School in the city of Winder, killing two teachers and two pupils, investigators say. Nine others were injured.

He was arrested on campus and will be prosecuted as an adult.

Police have identified the victims as teachers Christina Irimie and Richard Aspinwall and 14-year-old students Mason Schermerhorn and Christian Angelo.

In a news conference, Georgia Bureau of Investigation Chris Hosey said the gun used was an "AR-platform style weapon".

In a statement, the FBI said its National Threat Operations Center had alerted local law enforcement in May 2023 after receiving anonymous tips about "online threats to commit a school shooting at an unidentified location and time".

The agency said that within 24 hours investigators had determined that the threats had originated in Georgia.

Sheriff's deputies interviewed the boy and his father, who "stated he had hunting guns in the house, but the subject did not have unsupervised access to them", the FBI said.

The suspect, who was 13 years old at the time, denied making the online threats and officials "alerted local schools for continued monitoring of the subject".

"At the time, there was no probable cause for an arrest or to take any additional law enforcement action on the local, state or federal levels."

Sheriff Jud Smith described the attack as "pure evil" and said officers were on scene within minutes of receiving 911 calls at 10:20 local time (14:20 GMT).

Two officers assigned to the school "immediately encountered the subject", the sheriff said, adding that the boy "immediately surrendered".

The boy has been interviewed and spoke with investigators once while in custody, Sheriff Smith said.

The sheriff added that no motive had been identified and that law enforcement did not know of "any targets at this point".