The 17-year-old suspect is a student at Heritage High School in Menifee, but police said the threats weren't about a specific school.
The investigation began around 1:55 a.m. on Saturday morning when someone tipped authorities off to a group message chat on social media in which the suspect allegedly made those threats. Officials said the evidence included screenshots of the messages in the group chat.
Detectives said they served a search warrant at the suspect's home and when they questioned the suspect, they found a ghost gun tucked into his pants, as well as a set of brass knuckles.
He was arrested on suspicion of possession of brass knuckles, an unregistered firearm and making criminal threats.
Detectives said an extensive search was done at the suspect's home, and although ammunition was found inside, no further firearms were located. They said they're working to determine how the suspect came to be in possession of the ghost gun.
The Perris Unified School District issued a statement alerting parents about the incident and urged parents to pay attention to what their children are doing online.
"Parents and guardians, please take the time to talk with your students about the appropriate use of social media," said Candace Reines, the deputy superintendent. "All threats of violence are taken seriously and we will continue to work diligently with our law enforcement partners to pursue any person of interest."
Classes were not canceled at Heritage High School this week, but some students decided not to come to school.
"Every school I've been to they've had school threats," said one student outside the campus. "It's just scary, so I think I'm going to move to online school because this is just outrageous."
A woman who was waiting to pick up her granddaughter said it's important to recognize the important actions of the person who alerted authorities to the online threats.
"If you see something, tell someone... And that's exactly what this person did. And I think it helped in the long run from anything serious happening here."