RonBailey/iStock(LOS ANGELES) -- A 13-year-old boy was taken into custody after allegedly threatening a shooting at a Los Angeles County middle school, authorities said Friday.

The alleged plot for a Friday shooting at Animo Mae Jemison Charter Middle School was thwarted on Thursday, said Los Angeles County Sheriff Alex Villanueva.

A search warrant was obtained and investigators seized an AR-15, 100 rounds of ammunition, a list of students and staff, and a hand-drawn map of the school, authorities said.

Multiple students overheard the threat, Villanueva said, and teachers emailed the administration about their concerns. The administrators contacted deputies immediately, he said.

"The fact that people stepped forward" and reported what they heard allowed authorities to "prevent a possible tragedy today," said the sheriff.

The gun is unregistered, the sheriff said at a news conference on Friday.

Investigators are working to determine its origin, Villanueva said, adding that it does have a serial number.

The 13-year-old was taken into custody without further incident, authorities said.

This thwarted shooting comes one week after two students were shot and killed at Saugus High School, which is also in Los Angeles County. Three more students were shot and injured in the Nov. 14 attack, which was allegedly carried out by a classmate.

This is a developing story. Please check back for updates.

Copyright © 2019, ABC Audio. All rights reserved.