The father of a teenager who shot and killed four people at a high school in the US state of Georgia has been sentenced to 15 years in prison for murder, manslaughter and other charges.

Colin Gray, 55, was found guilty in March of a series of charges stemming from the 2024 attack that left two teachers and two students dead in Winder, Georgia.

His son, Colt Gray, 16, pleaded guilty to the murders last week and investigators said the rifle he used was a gift from his father.

Colin Gray was “the only person who could have prevented” the shooting from happening, prosecutors said.

The attack at Apalachee High School outside the city of Atlanta claimed the lives of Christian Angulo, 14, Mason Schermerhorn, 14, Richard Aspinwall, 39, and Cristina Irimie, 53.

The prosecution of Colin Gray marks the third time an American father has been held criminally responsible for a mass shooting carried out by his son, according to CBS News, the BBC’s US partner.

Judge Nicholas Primm handed down the sentence Thursday, giving the defendant 15 years for each second-degree murder conviction and 10 years for each involuntary manslaughter conviction, all to be served concurrently.

Georgia prosecutors had asked for the maximum sentence of 80 years in prison, while the defense asked the judge for a lighter sentence of 10 years.

Judge Primm spoke directly to Gray before announcing his sentence, admonishing him for not sending his son to counseling, as well as for failing to monitor his online activity and locking up guns in the house.

“It’s clear you failed as a father,” he said. “The warning lights were flashing more and more intensely… and you didn’t do the simplest things to prevent it.”

But Primm also acknowledged that Colin Gray “did not seek to harm anyone” and “did not pull the trigger.”

During the trial, the jury heard how the father had bought his son an AR-style rifle for Christmas the year before the attack, even though the boy had been questioned by police just seven months earlier about online threats to commit a school shooting.

Prosecutors argued that he ignored numerous warning signs, including a notebook detailing how his son planned to kill students and teachers.

“After seeing sign after sign of his son’s deteriorating mental state, his violence, his obsession with the school shooter, the defendant had plenty of warning that his son was a bomb waiting to go off,” Barrow County Assistant Prosecutor Patricia Brooks told jurors.

“And instead of disarming him, he gave him the detonator.”

His lawyers tried to shift the blame to his son.

“This is the person who walked into the high school and shot and killed four people he didn’t even know and injured dozens more,” his attorney, Jimmy Barry, told jurors, referring to the boy.

“This is the person who needs to be punished. He made a conscious decision about this, a secret decision.”

Charges against the parents of a school shooting suspect are relatively new in the United States, and at least two other cases have recently gone to trial.

In April 2024, the parents of a Michigan teenager who killed four students with a gun they had purchased for him just days before the shooting were sentenced for their role in the attack.

The case was widely reported to be the first time that the parents of a child who had carried out a mass shooting in the United States were held criminally responsible.