Georgia school shooting suspect kept gun in backpack, hid in bathroom before attack: GBI

State investigators are revealing new details surrounding the gun a 14-year-old boy allegedly used to kill two teachers and two students at his Georgia high school.

Colt Gray allegedly brought the AR-15-style rifle used in last week's shooting -- a Christmas present from his dad, according to sources -- to school on his own, the Georgia Bureau of Investigation said Thursday. Colt Gray rode the bus to Apalachee High School that day, the GBI added on Friday.

The long gun "could not be broken down," so the teen hid it in his backpack, the GBI said.

The morning of the shooting, Gray asked his teacher for permission to go to the front office and speak with an unidentified person, the GBI said. The teacher allowed him to leave and take his belongings with him, the GBI said.

The 14-year-old then went to the bathroom and hid from teachers, and later allegedly took out the rifle and started shooting, according to the GBI. Colt Gray was also armed with a knife, according to the GBI.

Colt Gray is accused of killing four people and injuring nine others at Apalachee High School on Sept. 4.

Seven of the nine people who were wounded suffered gunshot wounds, the GBI clarified on Thursday.

The school year started on Aug. 1, and Colt Gray was enrolled at Apalachee High School on Aug. 14, the GBI said. Between Aug. 14 and the day of the shooting, the teenager missed nine days of school, the GBI said.

Colt Gray is charged with four counts of felony murder. More charges will be filed, prosecutors said.

The teen's father, Colin Gray, is charged with four counts of involuntary manslaughter, two counts of second-degree murder and eight counts of cruelty to children, the GBI said. He is accused of knowingly allowing his son to possess the weapon used in the shooting, according to the GBI.

Investigators believe Colt Gray received the AR-style gun used in the shooting as a Christmas present from his father, according to sources.

Colt Gray and Colin Gray both made their first court appearances on Friday. Neither has entered a plea and both are set to return to court on Dec. 4.