SOUTH WHITTIER (CBSLA) — An alleged shooting plot at a high school in South Whittier was thwarted last week and a student and his brother have been arrested after a stash of weapons and ammo were found in their home, the Los Angeles County Sheriff’s Department reports.

weapons Student Arrested In South Whittier School Shooting Plot After Security Guard Overhears Threat

A stash of weapons that Los Angeles County Sheriff’s officials say were found at the home of an El Camino High School student who was arrested in a school shooting plot. (CBS2)

A 17-year-old boy was overheard by a school resource officer following a lunch break Friday threatening to “shoot up” El Camino High School “sometime in the next three weeks” Sheriff Jim McDonnell said at a news conference Wednesday.

The officer who heard the threat, Marino Chavez, contacted deputies, who began an investigation which lead them to the suspect’s Norwalk home, where they found two AR-15 rifles, two handguns and 90 high-capacity military-grade magazines.

“He (the suspect) did say that he was just kidding, that he did not mean it,” Chavez said. “I said, ‘well, you can’t say those things on campus.’”

“I’m not a hero, just doing my job every day,” Chavez told reporters.

Officials said the threat had followed a disagreement between the suspect and a teacher over his headphones, which are not allowed during class.

When asked by reporters whether the threat of a shooting appeared real, McDonnell answered, “The indications were, he was moving in that direction.”

“We found ammo in the kid’s room, loaded magazines,” Deputy Martin Maciel told reporters. “One of the weapons we recovered from the hallway, it was unsecured, it had no lock, and there were two loaded magazines right next to it. The other weapons were found in the garage did not have a door and was not secured.”

The suspect’s 28-year-old brother, Daniel Barcenas, an Army veteran, told deputies that the guns were his. One of the two rifles was unregistered, McDonnell said.

The teen suspect, who was not named, was arrested Friday for making criminal threats. McDonnell said the boy had an “extensive discipline history” at the school.

His brother, Barcenas, was arrested Tuesday night on multiple charges, including possession of an assault weapon, import of high-capacity magazines, criminal storage of firearms, failure to register a personal handgun and possession of an assault weapon and a thumbhole stock.

The two brothers lived at the home with their parents. It’s unclear whether the parents knew about the weapons, Maciel disclosed. The investigation is ongoing.

The weapons were “readily available,” McDonnell added.