What to Know Deputies responded to a report of a shooting threat Thursday at a Willowbrook elementary school

A rifle, ammunition and target list were among items seized at the boy's home

Staff members credit other students with reporting the threat

An AR-15 rifle, 100 rounds of ammunition and a list of intended targets were seized as part of an investigation into a shooting threat at a Los Angeles middle school, the Los Angeles County Sheriff's Department said Friday.

Deputies also found a hand-drawn layout of the school in what was described by authorities as an averted school shooting. The weapon was found at the home of a 13-year-old boy, who was arrested on suspicion of making criminal threats.

The threat investigation began Thursday after deputies responded to a report of a student who threatened to shoot staff members and other students at Animo Mae Jemison Charter Middle School in the Willowbrook area. A spokesperson for the school said other students notified staff members about the threat.

"We moved quickly to ensure that no harm came to our students," the statement said. "Our students did everything right by raising concerns with adults."

The weapon was not registered, but it does have a serial number, said LA County Sheriff Alex Villanueva.

The student under arrest made the threats on campus Thursday, he said.

"Multiple students overheard the school threat on campus and teachers emailed the administration about concerns raised by the students," Villanueva said. "School officials contacted the sheriff's department immediately."

The arrest comes about a week after a 16-year-old student opened fire at Saugus High School in Santa Clarita, killing two classmates and injuring three others. In that case, the shooter used an kit gun, which would likely skirt California's tough gun laws that require a background check before the purchase of a complete factory-made weapon.

During Friday's news conference, Villanueva said the department has been notified of a series of threats since the Nov. 14 shooting at Saugus High School. Another threat was made at Pete Knight High School in the Palmdale area north of Los Angeles. Covina police beefed up staffing Friday at Charter Oak High School in response to a possible threat targeting that school.

"With all incidents like these, we ask all Los Angeles County residents that if they see or hear something to say something," Villanueva said. "In this case, the fact that people stepped forward to say what they had heard led us to be able to prevent a tragedy today."