REDWOOD CITY, Calif. -- Thanks to a single voice speaking up, a potential school attack was prevented, according to a nonprofit created after the tragic Sandy Hook Elementary School shooting.

Police in Atherton, California were contacted by the nonprofit Sandy Hook Promise on Sept. 10, who claimed they received a tip that a former student at an area high school had posted concerning content to Instagram referencing the high school.

Police locked down the Menlo-Atherton High School campus in addition to a nearby middle school for an hour until the student was located. The investigation is ongoing, police say.

A mother is making it her life's mission to prevent tragedy. Nicole Hockley's son Dylan was one of 20 children killed in 2012 at the Sandy Hook Elementary School shooting . Hockl

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