ATLANTA – The 14-year-old boy accused of fatally shooting four people and wounding nine others at his Georgia high school last month meticulously planned the attack in a notebook that included estimated casualty counts and sketches of the hallway and classroom where the deadly shooting took place, state investigators said Wednesday.

Investigators also revealed that Colt Gray, the suspected shooter in the deadly Sept. 4 shooting at Apalachee High School in Winder, Ga., maintained a “shrine” in his bedroom to previous school shootings, which investigators said included a photo of Nikolas Cruz, the gunman in the 2018 school shooting in Parkland, Fla.

Testifying at a preliminary hearing for Colin Gray, the suspect’s father, who is also charged in the attack, an agent with the Georgia Bureau of Investigation said the elder Gray told investigators that he had questioned his son after he noticed Colt Gray had replaced a photo of a rock musician hanging on his bedroom wall with a photo of Cruz.

Speaking to law enforcement after the shooting, Colin Gray recounted how he had asked his son who the man was in the photo. “Dad, you really don’t know who that is?” Colt Gray allegedly replied.

“No, son, I don’t,” Colin Gray allegedly told his son.

Kelsey Ward, a GBI special agent, said Colin Gray told her that he “dropped” the subject but later pressed his son again about the image. “Colt explained it was Nikolas Cruz, a previous school shooter,” Ward testified, recounting what Colin Gray told investigators.

When Colin Gray asked his son why Cruz was on his wall, Colt Gray allegedly said that he “just” was. “There wasn’t any further discussion about that,” Ward said, recounting what Gray told law enforcement.

The hearing for Colin Gray came one day before prosecutors are expected to seek formal indictments against both Colin and Colt Gray from a Barrow County grand jury. Colin Gray’s attorneys had asked a judge to hold a preliminary hearing in his case to determine whether prosecutors had enough evidence to move forward with charges against him.

After a roughly 90-minute hearing Wednesday morning, Barrow County Chief Magistrate Judge Caroline Powers Evans found “probable cause” for the case against Colin Gray to proceed.

Colt Gray is charged as an adult with four counts of felony murder, with additional charges expected this week. He faces life in prison if convicted.

Authorities arrested and charged Colin Gray, 54, two days after the deadly shooting, accusing him of “providing a firearm” to his son even as he had “knowledge that he was a threat to himself and others.”

The elder Gray is facing two counts of second-degree murder, four counts of involuntary manslaughter and eight counts of cruelty to children. He faces as much as 180 years in prison if convicted.

Neither Gray has entered a formal plea in the case.