The father of the Georgia school shooting suspect has been arrested and charged with two counts of second-degree murder.
Colin Gray is also accused of four counts of involuntary manslaughter and eight counts of cruelty to children.
The charges stem from him allowing his son to possess a weapon, authorities said.
Two teachers and two students were killed in the attack at Apalachee High School in Winder, 50 miles northeast of Atlanta, on Wednesday.
Nine others – one teacher and eight students – were wounded in the shooting. They are expected to make a full recovery.
Colt Gray, 14, surrendered when “engaged by school resource officers inside the school”, Barrow County police said.
He is accused of committing the fatal shootings with an assault-style rifle outside his algebra classroom.
He has been charged with four counts of felony murder.
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What we know about Colt Gray
School shooting victims named
Father and son questioned by police last year
Following a tip off from the FBI, Colt Gray and his father were interviewed last year in connection with online threats about a school shooting made on the gaming platform Discord.
They denied making the comments, investigators said.
The case was closed after neither Gray could be connected to the Discord account, while no grounds were found to confiscate the family’s guns, according to police reports released by the sheriff’s office.
Information on the Discord account – which had profile information in Russian and a digital evidence trail indicating it had been accessed in different Georgia cities and Buffalo, New York – was “inconsistent”, an investigator said.
“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.
“We did not drop the ball at all on this. We did all we could do with what we had at the time.”
At the time, Gray’s father told officials he had hunting guns locked in a safe in the house and his son did not have access to them.
Colin Gray also said his son had struggled with his parents’ separation and often got picked on at school.
“He knows the seriousness of weapons and what they can do, and how to use them and not use them,” Colin Gray said, according to a transcript of the interview.
Gun found next to body in school
Student Lyela Sayarath said she heard 10 to 15 gunshots during the shooting.
Kassidy Reed, 17, joined classmates seeking counselling on Thursday and said she had struggled to sleep.
After the shooting, she said she saw blood in the hallway and what looked like a disassembled firearm lying next to a body.
“The first thing you wake up and think about is like, somebody lost the coach, somebody lost their dad, somebody lost their best friend,” she said.
Neither body camera videos nor audio will be released to “protect the integrity of the investigation”, the sheriff’s office said.
Classes at the school were cancelled on Thursday, though some people arrived with flowers.