The mother of the 14-year-old accused of killing four people at Georgia's Apalachee High School testified Monday that her son's behavior was "aggressive and unpredictable" in the year before the Sept. 4, 2024, shooting, as prosecutors seek to hold his father criminally responsible for allegedly allowing him access to a weapon.

Colt Gray is accused of opening fire at the Barrow County high school northeast of Atlanta, killing Mason Schermerhorn, 14; Christian Angulo, 14; and teachers Richard Aspinwall, 39; and Cristina Irimie, 53; and wounding nine others, authorities said.

He has been indicted on dozens of charges, including murder and aggravated assault, and prosecutors have said he is being prosecuted as an adult. A separate case against him remains pending.

His father, Colin Gray, is on trial facing 29 felony counts, including second-degree murder and involuntary manslaughter, as well as additional counts tied to endangering children. Prosecutors argue he ignored warning signs and failed to secure firearms in the home.

Defense attorneys have argued there was no way for the father to have foreseen the attack and that the teen concealed his plans.

Marcee Gray, the estranged wife of Colin Gray, told jurors that her son, Colt Gray, changed dramatically after moving in with her in the summer of 2023.

"He had a lot of anger inside, and he was very aggressive and unpredictable," Marcee Gray said during her testimony. 

"So much so that I ended up relocating his little sister across town to my parents' house because I didn't want to leave her there alone with him," she continued. "And then his little brother basically just never left my side."

Marcee Gray testified that in the months before the shooting, her son damaged TVs, broke windows, carved surfaces with knives, and wrote on walls, and she said she sought help as his behavior escalated.

After police were called, she said, Colt Gray returned to live with his father.

"I was trying to get him sent, you know, to juvenile detention," she said. "And once he had him convinced of that, Colt refused to talk to me, he just wanted to go back with his dad."

The father's case is part of a growing push by prosecutors in several states to pursue criminal charges against parents when a child's gun violence is tied to alleged failures in supervision, safe storage, or access to weapons. The Michigan convictions of the parents of the 2021 Oxford High School shooter are often cited as a landmark precedent.

Last week, student survivors described the terror of the shooting in testimony that prosecutors say underscores the harm they allege was made possible by easy access to a rifle and ammunition.

On Tuesday, 14 students testified, including Nautica Watson, who recalled passing out after being shot in the leg, and William Cariker, who sent a text as the gunman approached: "There's a school shooting if I don't make it I love you all."

• Trial Begins for Father in Apalachee High Shooting
• Trial Opens for Father of Accused Georgia School Shooter