Detectives and school resource officers immediately opened an investigation and eventually identified the suspect as a 17-year-old Gunn student. At about 2:45 a.m. on Friday, police contacted the student at his or her home in Palo Alto and safely took the teen into custody for a mental health evaluation. Police searched the home and found a "realistic-looking replica handgun that shoots BBs" in the student's room.

The threat was several paragraphs long, police said, and "referenced the author being in possession of a handgun and desiring to shoot students." The message "implied that it had been written by a Gunn High School student," the release states.

Police received an emailed tip shortly after 9 p.m. on Thursday from moderators of a public Facebook group about a threat, which had been submitted anonymously to the group through an online form, of a shooting to occur at Gunn sometime on Friday, according to a press release. After seeing the submission, the moderators forwarded it to the police's email tip line, and did not post the threat on the Facebook page.

The 17-year-old was taken in for a mental health evaluation. He or she may face criminal charges, police said.

In a message to the Gunn community on Friday, Laurence wrote that the school and police department determined it was safe for Gunn to be open on Friday.

This incident is a "good reminder," Austin said, of why the district wanted to invest in this position and put more of a focus on school safety.

Jacobs' position was approved by the school board in August to bring more oversight to security and safety efforts across the district's schools.

Superintendent Don Austin said Friday morning that he and other top administrators, including Deputy Superintendent Karen Hendricks, Safety Manager Mike Jacobs, Gunn Principal Kathie Laurence and the district's technology department, worked closely with police overnight to help identify the student.

"We applaud the moderators of the Facebook group for identifying this threat and reporting it to us so we could open an investigation and find the person responsible," police said.

The police department encouraged anyone who sees something suspicious, whether in person or online, to promptly report it to their local law enforcement agency.

The school district has also started its own investigation into the incident, Austin said.

"Any event of this nature can be unsettling. In addition, we know that this time of year can be stressful for students and families as finals and winter break approach," she wrote. "The Wellness Center and counselors will be available for any students who need support today at Gunn High School."

• Bay Area Clinical Associates serves youth through age 25, takes insurance, and has offices in San Jose, San Mateo and Oakland. Fill out the online appointment request form at baca.org and someone will contact you within 48 hours.

Anyone with information about this incident is asked to call the police department's 24-hour dispatch center at 650-329-2413. Anonymous tips can be emailed to [email protected] or sent by text message or voicemail to 650-383-8984. Tips can also be submitted anonymously through the police's free mobile app, downloadable at bit.ly/PAPD-AppStore or bit.ly/PAPD-GooglePlay .

This is the second shooting threat related to Gunn and made through social media this year. In August, police took into custody a 14-year-old student who allegedly threatened a shooting on campus through comments left on a police department Instagram post.

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Gunn High School student taken into custody for alleged online shooting threat

Facebook group moderators forwarded alarming submission to police