SAN RAMON (CBS SF) — Police and school officials in San Ramon confirmed Thursday morning that threatening graffiti found at Iron Horse Middle School led to a lockdown of the campus for over two hours, according to authorities.

The San Ramon Unified School District Twitter account posted about the incident shortly before 11 a.m. Thursday. Graffiti was discovered on a bathroom wall that read “school shooting at 12 p.m.” The middle school located at  12601 Alcosta Boulevard was quickly put on lockdown and authorities were called.

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San Ramon police and school district officials are investigating the incident. Police will provide an increased officer presence on the campus for the rest of the day out of an abundance of caution.

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Officials later announced that there were  15 district and police personnel stationed around the campus to provide additional security.

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San Ramon police confirmed that the lockdown had been lifted as of shortly after 1:15 p.m.