Authorities said the boy had two accomplices, a boy and a girl. They are accused of helping the suspect conceal evidence.
After the gun discharged, the suspect ran into a bathroom and exchanged shirts with someone, then handed over the backpack for someone to get rid of it, according to police.
Suspect admits to possessing gun
"He has admitted bringing a gun to the school," said Capt. William Hayes of the Los Angeles Police Department. "He has discussed the incident with us, and as we've indicated, it appears that it was accidental."
According to the LAPD, the suspect somehow acquired a 9mm Beretta semiautomatic handgun, similar to the one used by Los Angeles police. Officials said the suspect's own mother didn't know he had it.
The student allegedly told investigators he ditched the magazine of ammunition as he fled on campus. It still has not been recovered.
The suspect, who's from Compton, was booked on charges of assault with a deadly weapon. He was transported to a Downey juvenile detention facility. The suspect had already been on probation for a fight at the school last year.
Victims continue to improve
The gun discharged one bullet, striking a 15-year-old boy in the neck, leaving him seriously wounded.
Officials said the boy is in good condition and was to be released Wednesday night.
A 15-year-old girl was hit in the head by the same bullet and she is in critical condition. Doctors said she opened her eyes Wednesday morning and responded to commands, which they said is a promising sign.
"She does respond to commands and directions and is able to move both sides of the body, but one better than the other," said Dr. Gail Anderson, chief medical officer at Harbor-UCLA Medical Center. "It's still too early to tell what sort of results we're going to have over the next few hours and next few days."
School security criticized
Extra security and counselors were on hand at the school Wednesday.
Students said that as the campus was on lockdown, the suspect ran into another classroom.
"He ran in and we had no idea he was the shooter," said Lamont Cornelius, a student attending the class the suspect ran into. "He came in pretty innocent, quiet, and I'm like, 'What happened?' because we were inside the classroom and we weren't sure why we were on lockdown. We were asking him what was the idea of the lockdown. I guess he was too scared to tell anyone."
But the suspect wasn't scared to tell people he was bringing a gun to school, according to several students.
"More than a few people told him that gun is going to get you in trouble," said student Semaj Elam. "He didn't want to listen and this is what happened. Everybody learned their lesson."
"Him being an angry kid, I have a good idea that he might have been in somewhat of a bullying situation," Cornelius said.
Meanwhile, investigators are still searching for the backpack that is the key evidence in the case. Police said the suspect was able to get rid of the backpack before they were able to bring him into custody.
During all the chaos, a teacher in the room dialed 911. The teacher told the operator, "I'm a teacher at Gardena High School. We just had a shooting on campus at Gardena High School. We need paramedics. We have two minors down due to gunshot wounds."
Meanwhile, the Los Angeles Unified School District's incoming superintendent John Deasy said Gardena High School did not follow district policy that requires random weapons searches every day.
Students waited in long lines to enter the school as many students were searched with metal detectors Wednesday.
"It's just crazy, I never thought this would happen here," said student Shaqiel Wilson.
This security was not in place on Tuesday. The incoming superintendent said the school's security was not up to par.
"It's a daily expectation for random searching," Deasy said. "The school did not implement it fully. We are dealing with administrative review for anybody who didn't follow that and any changes that are currently being reviewed by a police chief."
The school's police chief is now considering walk-through metal detectors in schools and better emergency communication with parents.
"If it was not covered by the media, this incident would have gone by and we would not have known about it," said parent Deborah Reid.