Classes were canceled at Sunny Hills Highs School in Fullerton on Wednesday morning after a suspicious note was found taped to a door of an administration building on campus, police said.
A school staff member reported finding the note at 6:38 a.m., prompting officers to search the campus and send students home for the day, said Lt. Robert Bastreri of the Fullerton Police Department.
Police said the note detailed a specific threat to an unnamed student - the message was not related to terrorism or a bomb threat.
"All kids here come to get education and feel safe, and that's not how we all feel today," Armando Rogel said. "If it's a joke, it is not funny. No one is laughing, you know? People are scared for their life right now, and everyone hopefully be with God."
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Nothing suspicious was found during the search, police said. The school will reopen Wednesday.
No other Fullerton schools were affected.
The threat was made a day after hundreds of Los Angeles Unified School District campuses were closed after school board members received an email threatening violence against multiple campuses. The threat was determined to be a hoax.
Oleevia Woo contributed to this report.