MILL VALLEY (CBS SF) — A report about a person wearing a black mask and possibly carrying a rifle behind Tamalpais High School in Mill Valley caused a lockdown and shelter in place Monday afternoon, police said.

Officers responded around 1:50 p.m. to a report about a possible gunman wearing black clothes on Almonte Boulevard around 1:50 p.m. Another person reported seeing a suspect wearing a mask and similar clothing near parked vehicles but a gun was not seen, police said.

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Police and Marin County sheriff’s deputies checked the area for a gunman and a white car, and authorities issued a shelter in place order that included a lockdown of the high school and Mill Valley Middle School.

Law enforcement agencies throughout the county searched the high school and surrounding area, and witnesses confirmed the suspect and vehicle left the area, police said.

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Mill Valley Middle School students were released at their regular 2:30 p.m. time, and after an extensive search of the high school, the lockdown and shelter in place was lifted there, police said.

Police said the suspicious person was not identified or located, and rumors about an associated armed bank robbery were unfounded. The Marin County Sheriff’s Office is investigating the case.

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