The gunfire erupted in a classroom at the school in the Westlake neighborhood shortly after the opening bell and caused numerous students to run from the area, Los Angeles Police Officer Drake Madison said.
A man was found dead in his auto from a gunshot wound early Saturday morning in South Los Angeles, police said.
This was at least the third school shooting in recent weeks in the United States.
The district has a policy that requires every middle and high school campus to conduct daily random searches by metal-detector wands at different hours of the school day for students in the sixth grade and up.
An LAPD spokesman confirmed that they have one suspect, a female student, in custody.
The suspect was arrested at the scene and charged in juvenile court yesterday with felony counts of being a minor in possession of a firearm and having a weapon on school grounds.
Authorities affirmed that the incident was unintentional, pointing out that the two students, a boy and a girl, sustained serious head and wrist injuries and were transferred to hospital. The girl holding the firearm "didn't mean to" shoot the 15-year-old girl, he said, according to the station. Three others had superficial face or head injuries, some from broken glass.
In a morning news conference, Los Angeles School Police Chief Steve Zipperman said he did not know how a young person got access to a gun and brought it to campus, but warned gun owners to keep their weapons secure and away from children. "They thought it was a fake gun".
The shooting was reported to police Thursday at 8:55 a.m.
Gloria Echeverria stood near a line of police tape preventing people from approaching the school, waiting for news about her 13-year-old son.
Los Angeles police kept parents updated on Twitter and in a meeting outside the school, telling them if they had not heard from their child they should assume they were safe and well.
None of the identities of those who were injured have been released.
"We will attend to the needs of these students who witnessed this very carefully, with the understanding this is very traumatic", he said.
We are fully cooperating with the Los Angeles Police Department in its investigation of this matter.
The Los Angeles Police Department, Los Angeles Fire Department, Los Angeles School Police and District leadership immediately responded, and we followed protocols to ensure the safety and well-being of the Castro Middle School community.