Videos taken inside Apalachee High School in Winder, Georgia, following Wednesday's mass shooting show a sense of calm amid the chaos.
Sophomore Alexsandra Romero, 15, was sheltering with classmates inside a classroom when she caught footage of law enforcement officers entering the room and directing them down a corridor to exit.
"Single file line down this aisle right here after this deputy," an officer is heard saying. "Hurry up now, come on, let's go. We got a whole school to get evacuated, people, come on now."
Romero told The Atlanta Journal-Constitution she thought what was happening was a drill.
GEORGIA HIGH SCHOOL SHOOTING: 4 DEAD, 1 SUSPECT IN CUSTODY, AUTHORITIES SAY
"I can just remember my hands were shaking," Romero said. "I felt bad because everybody was crying, everybody was trying to find their siblings."
Another video captured by the teen on her way out of the school shows a body covered by a sheet with blood surrounding it and firearms on the floor.
WHO IS THE ALLEGED GEORGIA SCHOOL SHOOTER? WHAT WE KNOW
Authorities identified the four victims who were killed as two teachers and two students.
Georgia Bureau of Investigation Director Chris Hosey identified the teachers as Richard Aspinwall and Christina Irmie, who both taught math, and the students as Mason Schermerhorn and Christian Angulo, both 14.
Nine others were taken to various hospitals with gunshot wounds.
On Wednesday, authorities identified Colt Gray, now 14, as the suspected shooter. Gray surrendered to authorities and was taken into custody following the rampage.
Gray had been on the FBI's radar as a possible threat since last year, the agency confirmed.
"At that time, there was no probable cause for arrest or to take any additional law enforcement action on the local, state, or federal levels," the FBI said.
Fox News' Stepheny Price, Gabriele Regalbuto and Louis Casiano contributed to this report.
