Though most appeared to be hoaxes - "jokes", as several suspects called them - administrators, police and school resources officers have been on high alert, looking out - warily - for students motivated to threaten or engage in similar behavior.
The police department and school district are positioning this case as a learning lesson for parents, as well as students and school faculty. The boy was taken to a care facility. The firearms were not secured in the home, he said.
The student apparently indicated he was going to "shoot up the campus", though he didn't issue a threat against any specific individuals, according to Jacobsen.
"I'm not a hero", said Chavez, who had never spoken with the student before.
Chavez said he asked the student about the threat, and the teen confirmed that he made it but was just kidding and didn't mean it. The school is located in Whittier, about 20 miles east of Los Angeles.
A search turned up two AR-15 rifles, two handguns and 90 high-capacity magazines, each capable of holding 30 rounds.
Authorities says a 17-year-old student has been arrested after threatening to open fire at a California school and his adult brother faces five weapons charges after weapons were found in their home. One of the rifles was not registered, which is a felony in California, Sheriff McDonnell said. His older brother, Daniel Barcenes, a military veteran who claimed the guns belonged to him, was arrested on charges of possession of an assault weapon, thumbhole stock, import of high capacity magazine, possession of high capacity magazine, criminal storage of a firearm and failure to register a personal handgun.More news: Former Cyclone Gita hits New Zealand, emergency declared in Christchurch
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A national organisation that tracks school threats said it has recorded around 50 a day on average since the Florida shooting, compared with about 10 a day on average.
Chavez said it was after lunch break and students were returning to class when he heard the threat about a school shooting within the next three weeks. He had brought headphones to school, and students are not allowed to have electronic devices out during class time, district officials said.
Jacobsen says the school "felt there was enough there to call law enforcement". They also said he had ammunition and loaded magazines in his room.
McDonnell said this was the second threat at El Camino High, a continuation high school at 14625 Keese Drive in unincorporated South Whittier, in a week.
An alert security guard overheard a student threatening to open fire at his Southern California high school days after a massacre in Florida, and a swift investigation uncovered two AR-15 rifles and almost 100 high-capacity magazines at his home, authorities said Wednesday.
Sheriff's spokeswoman Nicole Nishida tells The Associated Press that deputies discovered "multiple guns and ammunition" after searching the student's home.
Officials have scheduled a news conference for Wednesday.