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.
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"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."
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.