ATLANTA (AP) — The 14-year-old who is accused of killing four people in a Sept. 4 shooting at Apalachee High School in Georgia started school two weeks late and then was absent for nine more days before the shooting, investigators said Friday.

Colt Gray was first enrolled at the high school northeast of Atlanta on Aug. 14, the Georgia Bureau of Investigation said. The first day of school was Aug. 1.

The late enrollment, combined with the absenteeism, show that the boy’s life may have been troubled. His mother, Marcee Gray, has said she and other relatives on her side of the family sought the school’s assistance the week before the shooting to get psychiatric treatment for her son.

Colt Gray is charged as an adult with four counts of murder, and District Attorney Brad Smith has said more charges are likely to be filed against him in connection with the wounded. Authorities have also charged his father, Colin Gray, alleging that he gave his son access to the gun when he knew or should have known that the teen was a danger to himself and others.

Here’s a timeline of what happened before, during and after the attack, based on statements by authorities and reporting by The Associated Press and other news media:

Aug. 1 — School starts in Barrow County.

Aug. 14 — Colt Gray is enrolled at Apalachee High School. Investigators say he was absent for nine additional days before the shooting,

Sept. 4, 8:15 a.m. — First period begins. Officials have not said what class Gray was scheduled for or whether he attended. Officials said he rode the school bus to Apalachee High School carrying a semiautomatic assault rifle hidden in his backpack. Investigators say Gray also had a knife.

Sept. 4, 9:38 a.m. — First period ends. Students have seven minutes to change to their next class.

Sept. 4, 9:45 a.m. — Second period begins. Student Lyela Sayarath said she briefly saw Gray in the algebra class where the two sat next to each other. Investigators say Gray left the classroom asking to go speak to someone in the front office, but instead took his backpack with the gun inside and hid in a bathroom.

Sept. 4, 9:50 a.m. — Marcee Gray, Colt’s mother, calls the high school from 200 miles (320 kilometers) away in Fitzgerald, Georgia, to warn that her son was having an “extreme emergency” after getting a text from Colt saying, “I’m sorry.” Marcee Gray said a counselor told her that an email earlier that morning from one of Colt Gray’s teachers said he had been talking about school shootings. Marcee Gray said she urged them to find her son to check on him. Call logs show the call lasted until 10 a.m.

Sept. 4, 9:45 a.m. to 10:20 a.m. — An administrator comes to the algebra classroom looking for a student with the same last name and a similar first name to Colt Gray, Sayarath and Barrow County Sheriff Jud Smith said. When the other student returns, he tells Sayarath that the administrator was actually seeking Colt Gray. In the meantime, the teacher is called on the intercom, Sayarath said.

Sept. 4, about 10:20 a.m. — Colt Gray approaches the door of the algebra classroom. As the intercom buzzes again, the teacher responds, “Oh, he’s here,” seeing Gray outside the classroom door, Sayarath said. When students go to open the door, which automatically locks from the inside when closed, Sayarath said they backed away. She said she saw Gray turn away through the window of the door and then she said she heard 10 or 15 consecutive gunshots. People are shot in the hallway and inside at least one classroom, as others in the halls scramble for safety. According to some students, the three teachers who are shot are trying to protect students.

Sept. 4, 10:23 a.m. — After multiple employees press wireless panic buttons embedded in their employee badges, the school goes into lockdown and a massive law enforcement response begins. Students in other classrooms who hear the gunshots begin texting and calling their parents and others.

Sept. 4, 10:26 a.m. — The two school resource officers assigned to Apalachee High School approach Gray in the hall, according to GBI Director Chris Hosey. Gray immediately surrenders and is taken into custody.

Sept. 4, about 11 a.m. — Law enforcement officers begin searching Colin and Colt Gray’s house east of Winder. At the school, officers go from classroom to classroom, first looking for more people with injuries or other shooters. Later, officers evacuate students to the football field as hundreds of parents rush to campus.

Sept. 4, about 1 p.m. — The school begins releasing students to parents to take them home.

Sept. 5 — Colin Gray, Colt Gray’s 54-year-old father, is charged with four counts of involuntary manslaughter, two counts of second-degree murder and eight counts of cruelty to children. Officials say Colin Gray allowed Colt Gray the access to the assault rifle even though Colin Gray knew his son was a danger to himself or others.

Sept. 6 — Colt and Colin Gray make initial appearances in court in Winder. Neither requests that the judge set bail. Colt Gray remains held in a juvenile detention center, while Colin Gray is in the Barrow County jail.

Sept. 10 — The 13,000 students at the Barrow County school district’s other schools return to class. Officials have not announced a restart date for the 1,900 students who attend Apalachee.

Sept. 11 — Lawyers for Colin Gray ask a judge to order that he be kept separate from the other inmates in the Barrow County jail for his safety, citing the “incalculable number” of threats of violence or death against him.