"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," the Georgia Bureau of Investigation said on X.
The father was charged with four counts of involuntary manslaughter, two counts of second-degree murder and eight counts of cruelty to children, the Georgia Bureau of Investigation said.
In that 2023 probe, the father said he had hunting guns in the house but that his son did not have unsupervised access to them, and the son denied 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.
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 in an interview. "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. He will be charged and tried as an adult, the Georgia Bureau of Investigation said.
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 before a Georgia Superior Court judge in Barrow County by video camera.