The 14-year-old charged with shooting up a Georgia high school last week brought a rifle into the school inside his backpack, authorities said.
Colt Gray brought the gun to Apalachee High School in Winder on his own on Sept. 4, the Georgia Bureau of Investigation (GBI) confirmed.
The assault-style rifle could not be broken down, but Gray hid it in his backpack, authorities added.
"It would have stuck out, but he had some things that made it concealed," Barrow County Sheriff Jud Smith told WSB-TV Atlanta.
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Gray was able to leave the classroom because he asked a teacher if he could go to the front office and speak to someone. The teacher allowed him to leave and take his belongings with him.
"Which was not uncommon. He asked to go up front and speak to someone at the front, and when you do that you take your belongings with you," Smith told WSB-TV, "so the teacher allowed him to leave."
Gray then went to the restroom, where he hid from teachers.
Later, he allegedly took out the rifle and began shooting, leaving two students and two teachers dead. Seven other victims had gunshot wounds, and two others suffered other injuries, police said.
The victims were identified as Richard Aspinwall, 39; Cristina Irimie, 53; and Mason Schermerhorn and Christian Angulo, both 14.
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Apalachee High School does not have metal detectors, GBI said.
The suspect's mother, Marcee Gray, called the school counselor the morning of the shooting to warn officials about a concerning message she had received from her son, she said in an interview with ABC News.
She said the last message she had received from her son was, "I’m sorry, Mom," and that his father had received similar texts – "I’m sorry" and "You’re not to blame for this."
Colt Gray has been charged with four counts of felony murder and more charges are expected.
His father, Colin Gray, 54, is accused of "knowingly allowing" his son to possess the weapon he used in the attack, police said. He was charged with two counts of second-degree murder, four counts of involuntary manslaughter and eight counts of cruelty to children.
