The 17-year-old, who has not been named because he is a juvenile, has been arrested and faces a charge of making a criminal threat.
Chavez told reporters that the teenager had remarked 'that within three weeks there would be a school shooting on campus'.
Chavez says the student said he was kidding and didn't mean it.
A few hours after Chavez raised the alarm, Los Angeles County sheriff's investigators found a cache of firearms, including two semiautomatic rifles, two handguns and 90 high-capacity magazines, at his home, reported the Los Angeles Times.
The school then reported the teen to authorities, who found two assault rifles in his home, including one that was unregistered, according to the AP.
The sheriff said the brother is facing charges of possession of an assault weapon and other violations and that the teen had an extensive disciplinary history at school. The other wasn't registered, a felony in California. While the actual credibility of those threats is questionable, school authorities prefer to take no chances in wake of the deadly Florida shooting that took the lives of 17 people.
CDC warns of salmonella infections traced to kratom
Kratom should not be consumed in any form, the CDC said, because the source of salmonella contamination has not been identified. Kratom contains alkaloids which bind with the same opiate receptors in the brain that prescription and street opioid drugs do.
A student allegedly threatened to bring a gun to El Camino High School after being told he couldn't have his headphones in class..
Sheriff Jim McDonnell credited "attentive" school resource personnel, as well as "diligent" investigators, with preventing what he said could have been a risky outcome. The student later said he was joking, Jacobsen said.
Deputies with the Norwalk sheriff's station responded to the school on Friday to investigate a criminal threats call issued by school officials at the warning of the security officer.
The alleged threat was overheard by a school security officer at El Camino High School, located in Whittier, California.
Sheriff's spokeswoman Nicole Nishida told the Associated Press deputies discovered "multiple guns and ammunition" after searching the student's home.
A sheriff's department news conference was scheduled for 10:30 a.m. Wednesday.