Monrovia High School and Monrovia Elementary were placed on emergency lockdowns Thursday afternoon after what police believe was a fake call reporting an active shooter, the city said.
The city of Monrovia said in a series of tweets that the high school was placed on lockdown after a 911 caller reported an active shooter on campus around noon.
Monrovia police responded to the campus and did a sweep, but had not found any evidence of a shooter nor any violence.
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Police said it may have been a "swatting" call, wherein someone places a fake call to police hoping to elicit a massive SWAT response, according to the superintendent's message.
The city said other school districts have received similar calls Thursday.
The city said after police concluded the sweep, the school would reopen and the school day would resume as normal.
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By 1 p.m., the elementary school campus was cleared by authorities.
Updates can be found on the school's website here.