The father of the teenager accused of shooting dead two fellow students and two teachers at his school in the US has been arrested and charged.

Georgia state officials said they had arrested 54-year-old Colin Gray in connection with this week’s shooting at Apalachee High School, in which nine people were also wounded.

Gray, who is the father of Colt Gray, 14, has been charged with four counts of involuntary manslaughter, two counts of second-degree murder and eight counts of cruelty to children.

The teenager has been charged with four felony counts of murder.

Georgia Bureau of Investigation director Chris Hosey said Colin Gray’s charges stemmed from him “knowingly allowing” his son to have a weapon.

CNN reports that the father told investigators this week he had purchased the gun used in the killings as a holiday present for his son in December 2023.

It follows the FBI saying on Wednesday that both Grays had been questioned by local officials in neighbouring Jackson County in 2023 in connection with an online threat to commit a school shooting, but there was no probable cause for their arrest.

UPDATE #2 – September 5, 2024:

In coordination with District Attorney Brad Smith, the GBI has arrested Colin Gray, age 54, in connection to the shooting at Apalachee High School. Colin is Colt Gray’s father.

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— GA Bureau of Investigation (@GBI_GA) September 5, 2024

In the 2023 probe, Colin Gray said he had hunting guns in his house but his son had no unsupervised access to them. Colt Gray making the threats online, the FBI said.

Georgia state and Barrow County investigators say the younger Gray used an “AR platform-style weapon”, or semiautomatic rifle, to carry out the attack in which two teachers and two 14-year-old students were killed.

It remained unclear how the shooter obtained the weapon.

Colt Gray remains in custody, while his father has also been arrested. Photo: AAP

The shooter’s ability to obtain the semiautomatic rifle, any signs warning that he would actually carry out a shooting, and his motive are focuses for investigators digging into the first US campus mass shooting since the start of the school year.

Jackson County sheriff’s investigators closed the case after being unable to substantiate that either Gray was connected to the Discord account where the threats were made, and did not find grounds to seek the needed court order to confiscate the family’s guns, according to police reports released by the sheriff’s office on Thursday.

“This case was worked, and at the time the boy was 13, and it wasn’t enough to substantiate,” Jackson County Sheriff Janis Mangum said.

“If we get a judge’s order or we charge somebody, we take firearms for safekeeping.”

The younger Gray was taken into custody shortly after the shooting at Apalachee High School. The GBI said he would be tried as an adult.

Gray was being held without bond at Gainesville Regional Youth Detention Center, Georgia Department of Juvenile Justice communications director Glenn Allen said on Thursday.

His arraignment is set for Friday morning before a Georgia Superior Court judge in Barrow County by video.

-with AAP