RIVERSIDE (CBSLA.com) — A 29-year-old man was in custody Monday for allegedly posting a threatening message online at the University of California, Riverside.

According to campus police, Anton Shirokov, of Riverside, posted a threat on Yik Yak Sunday, which raised concern of a possible shooting spree on campus.

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Officials said they received numerous calls from concerned campus community members in response to the post.

A campus-wide text alert was issued in response, however, campus police believed there was no credible threat to the community.

“We take every such threat seriously, and are fully investigating this posting,” explained spokesperson James Grant.

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The post has since been deleted, and authorities are working with Yik Yak to collect forensic evidence.

Shirokov turned himself into UCPD around 1:40 a.m., and admitted to posting the online threat as a joke.

A search warrant of his apartment subsequently located a set of brass knuckles.

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According to police, Shirokov is currently being held on a non-related weapons charge, and has apologized to the community for making the post.