A student’s anonymous tip helped prevent a potential school shooting at Menlo-Atherton High School in Atherton, leading to intervention by district officials and law enforcement, according to Sandy Hook Promise.

The nonprofit said Monday that a student flagged a peer’s Instagram post through its “Say Something Anonymous Reporting System.” According to Sandy Hook Promise, “posts included images of firearms, ammunition, and a mapped-out plan for attacking the school.”

On Sept. 10, the group’s crisis center alerted the Sequoia Union High School District’s response team, prompting a precautionary lockdown at Menlo-Atherton High School, as well as nearby Laurel School.

According to a statement posted by Atherton police on Tuesday, they went to the student’s home and said no weapons were recovered.

Police clarified that the post in question showed only ammunition magazines, not firearms. The individual accused of making the posts is a former Menlo-Atherton High School student who is now enrolled at another school.

“There were no firearms depicted,” police said. He has been placed on a psychiatric hold since the Sept. 10 incident.

This news organization reached out to the Atherton Police Department for specifics on potential charges and to ask if ammunition was found in the home, but was told no one was available for additional comment.

The department said in its statement that it was “grateful to the community, school staff, and our regional partners for their swift action and cooperation. We again remind the public that reporting suspicious activity is critical to maintaining community safety: If you see something, say something.”

“The Atherton Police Department continues to work closely with Menlo-Atherton High School, other law enforcement agencies, and the District Attorney’s Office as this investigation proceeds,” Atherton police said.

Jarrett Dooley, executive director of student services for Sequoia Union High School District, said the school is thankful the reporting system allowed local authorities to take swift action.

“We are proud partners with Say Something and Sandy Hook Promise. We are grateful that the anonymous student tip resulted in swift action by local law enforcement and school administrators to keep all students, staff and community members safe,” Dooley said.

Sandy Hook Promise, founded by family members of those killed in the 2012 mass shooting at Sandy Hook Elementary School in Newtown, Connecticut, operates the anonymous reporting system.

The program, available to students in grades 4—12, allows concerns to be submitted by app, text, phone or website. The system aims to provide safe and private reporting that can trigger interventions before tragedies occur.

Nicole Hockley, co-founder and CEO of Sandy Hook Promise, said the Bay Area case highlights the importance of vigilance.

“Sometimes we receive hundreds of tips about a potential threat. Other times, as we saw in California during this incident, it just takes one,” said Hockley, whose son Dylan was killed in the Sandy Hook shooting. “At a time where many feel powerless against gun violence, this student’s bravery proves that each of us has the ability to make a difference. Gun violence is not inevitable — it is preventable — and prevention begins when we recognize the signs and take action.”

In 2023, a mass shooting in Half Moon Bay left seven people dead, one of the deadliest shootings in recent San Mateo County history.