San Leandro High School was placed on lockdown Tuesday morning after graffiti was found on the campus threatening a school shooting, police said.
San Leandro police issued a community message shortly before 11:10 a.m. about the police activity at the school at 2200 Bancroft Ave.
Police are working with district and school staff to ensure safety on the campus and to systematically inspect the school grounds.
Students cannot be dismissed from the campus so police advised parents to not go there until officers confirm that no threat exists.
All other schools in the San Leandro Unified School District remain open, according to police.