SOUTH LOS ANGELES (KABC) -- Sheriff's investigators have arrested a 13-year-old student after responding to a call of a threat to shoot other students and staff at Ánimo Mae Jemison Charter Middle School in South Los Angeles, Undersheriff Tim Murakami announced Friday morning.

The undersheriff described the arrest in a tweet but did not immediately disclose details about the suspect.

According to Murakami, deputies from the Los Angeles County sheriff's Century station initiated the investigation, which led to a search warrant and the seizure of a AR-15 rifle, ammunition, "a list of intended victims and a drawing of the school layout."

In a separate case, a sheriff's task force took a suspect into custody on suspicion of dealing and possessing illegal firearms. That individual allegedly purchased parts on the internet and "had a ghost rifle -- fully auto, silencers, body armor," said the undersheriff, who apologized for the confusion that led to the conflation of the two investigations in initial news reports.