Colt Gray's mother had cited the Crumbley case when she urged that her son's access to guns should be cut off before the 2024 mass shooting, according to Barrow County District Attorney Brad Smith.
"We hope that (this conviction) moves the needle a little further," Smith told reporters.
"I think you saw in this case that the mother actually reviewed what happened in Michigan ... and she then, as a result of that, asked her husband to remove the weapons," Smith said.
"It could have ended this tragedy. So Michigan was able to move the needle to the point that almost stopped this tragedy," he said. "How many tragedies it did stop? We hope we move the needle a little further."
The jury deliberated for less than two hours before finding Gray guilty on all 27 charges.
He didn't appear to show outward emotions as the jury delivered its convictions.
After the jury was polled to confirm all the guilty verdicts, Gray, wearing a blue sport coat and khaki pants, was handcuffed and taken away by court security.
Judge Nicholas Primm didn't immediately set a date for sentencing, saying that "there are a lot of people that need to be notified and have a right to appear." Gray is facing up to 243 years behind bars.
Defense attorneys declined to answer reporters’ questions as they left the courthouse.
Colt Gray is accused of using the firearm his father should have secured to carry out the slaughter about 45 miles northeast of downtown Atlanta.
The younger Gray, who was 14 at the time of the shooting, remains in custody and a trial date has not yet been set.
Prosecutors accused Colin Gray of ignoring warning signs of his son's potential violence and allowing him access to the high-capacity weapon used at Apalachee High School.
Jurors were shown pictures of Colt's bedroom, which included pictures of school shooter Nikolas Cruz on the wall. Cruz killed 14 students and three staff members at Marjory Stoneman Douglas High School in Parkland, Florida, on Feb. 14, 2018.
The four slain in Georgia were Mason Schermerhorn, 14; Christian Angulo, 14; Richard Aspinwall, 39; and Cristina Irimie, 53.
Colin Gray, testifying on his own behalf, recounted incidents of his son feeling bullied at school and occasionally showing signs of rage.
Still, the dad told jurors he never considered Colt Gray to be a violent threat.
“I never thought that he would even have a thought process of bringing a gun to school or doing any kind of harm to anybody else. Well, on anybody at school,” the older Gray told jurors.
