This story was updated at 5:56 p.m. on Sept. 10, 2025 to include a message from Principal Karl Losekoot.
This story was updated at 5:20 p.m. on Sept. 10, 2025 to include statements from The Atherton Police Department, Principal Karl Losekoot, and accounts from Carlmont students.
M-A went into Secure Campus at the beginning of fifth period on Wednesday, following an anonymous tip claiming a former M-A student was making online threats.
In a statement sent to students, staff, and parents, M-A Principal Karl Losekoot explained that M-A received an anonymous tip on the See Something, Say Something tip line this afternoon.
The Atherton Police Department also released a statement explaining that the tip identified a former M-A student currently enrolled at a nearby high school as the source of the threats. After initiating an investigation, the Atherton Police Department was able to locate and detain the identified student. The former student, who is reportedly undergoing psychiatric issues, is currently being held at a medical facility.
Carlmont High School was also placed on Secure Campus at the request of the Belmont Police Department at approximately the same time. The order was lifted around 1:15 p.m., according to a ParentSquare message from the school.
While the Belmont Police Department has not yet disclosed the cause of the lockdown, multiple Carlmont students reported hearing rumors of a former M-A student who now attends Carlmont posting troubling content regarding both Carlmont and M-A.
Secure Campus is a precautionary measure against the threat of potential violence. This emergency response is less severe than a lockdown and occurs when a threat of violence occurs near campus or there is police activity in the surrounding area. During a Secure Campus, students and staff must remain inside and lock all doors, but are able to continue instruction.
At 12:55 p.m., Losekoot instructed students and staff via the intercom to stay in their classrooms and lock all doors and entrances into the school. At 1:27 p.m., Losekoot announced that the administration was “making progress and resolving the situation.” The Secure Campus officially ended at 1:59 p.m.
Losekoot sent out a message to parents through ParentSquare advising them not to come to school or call the office.
Due to its proximity to M-A, Laurel Lower Campus and Encinal School were also placed under Secure Campus this afternoon as a safety precaution.
The M-A Chronicle reached out to the Belmont Police Department but did not receive a response in time for the publication of this article.
Thank you for the excellent journalism.
As many of us parents in the community were searching for information, this team’s reporting and updates were one of the best sources of information. It’s also during a time when you yourselves were impacted. Kudos on the excellent reporting.