Police in Los Angeles have arrested a 12-year-old girl after a shooting at Sal Castro Middle School on Thursday. Two 15-year-olds were shot in a classroom; one boy, who was shot in the head, is said to be in critical condition. The other victim, a girl, was shot in the wrist. According to Los Angeles Fire Capt. Eric Scott, another woman, 30, and two children, 11 and 12, are also being treated for minor cuts sustained during the incident.

This is the third U.S. school shooting in just over a week; a 15-year-old boy in Kentucky killed two and wounded 14 on Jan. 23, the day after a 16-year-old boy wounded one girl in Texas.

The Sal Castro Middle School shooting was reported to police at 8:55 a.m. PST. Los Angeles School Police Chief Steven Zipperman assured the public late Thursday morning that the school was secured. “Our campus, while it’s on lockdown, is safe. There is no more safety threat to the students of this school,” he said. Police are reported to have found and confiscated the gun.

The L.A. Times writes that "investigators are still conducting interviews to determine whether the shooting was intentional," or, as LAPD deputy chief Robert Arcos says, a "terrible accident."

The school's regular dismissal time was not changed, although parents were permitted to bring their kids home early.