Harvard-Westlake High School in Los Angeles was closed on Friday after the prep school learned of an online threat from an alum, believed to be former Miami Dolphins offensive lineman Jonathan Martin.

A former Harvard-Westlake student made an indirect threat on Instagram, seeking revenge as a bully victim, police told multiple media outlets in Los Angeles. Officials reportedly sent an alert around 7 a.m. warning students of a “security risk” and closing the school’s two campuses in the city on Friday.

That student was identified as Martin by 12up.com’s Nick Brown. Brown shared a screen grab of Martin’s verified Instagram account that shows the disturbing image of a gun, surrounded by bullets, with the caption, “When you’re a bully victim & a coward, your options are suicide, or revenge.”

Former Dolphins OL Jonathan Martin with some seriously disturbing stuff on his IG story… pic.twitter.com/NaJ8a0BXze — Nick Brown (@NickyBeaster) February 23, 2018





According to ABC News producer Matt Stone, Martin was taken into custody on Friday:

BREAKING: @ABC confirms: Former Dolphins OL Jonathan Martin has been taken into custody — Matt Stone (@MattStoneABC) February 23, 2018





Martin was the subject of a much-publicized bullying incident during his second and final season with Miami in 2013. An NFL investigation determined that Dolphins teammates Richie Incognito, Mike Pouncey and John Jerry subjected Martin to “a pattern of harassment” in “a classic case of bullying.”

Incognito, Pouncey and two former Harvard-Westlake classmates were tagged in the screen grab of Martin’s Instagram story. The hashtags “HarvardWestlake and #MiamiDolphins were added to the gun.

“Last evening, we learned of an Internet post that mentions Harvard-Westlake by name,” school officials said in a statement on Friday, via KTLA. “Out of abundance of caution, and because the safety of our students, faculty, and staff is our top priority, we made the decision to close school today. We are working closely with law enforcement and will share more information when we are able.”

A former second-round pick out of Stanford, Martin did not play for the Dolphins after news of the bullying allegations went public. He played 15 games for the San Francisco 49ers the following season, starting seven of them, and was claimed off waivers by the Carolina Panthers in March 2015. He retired from the NFL at age 24 that summer, citing a back injury that would have cost him the 2015 season.

The NFL published a 144-page report from attorney Ted Wells, which included a series of distressing text messages from Martin to his parents alleging bullying throughout middle and high school, at Stanford and in Miami. He told his parents he suffered from anxiety and “really severe depression.” Martin wrote in 2013, “A therapist and medication won’t help me gain the respect of my teammates.”

Following his retirement from football, Martin wrote on Facebook that he attempted suicide on multiple occasions. “You let your demons go,” Martin shared upon retiring, “knowing that, perhaps, sharing your story can help some other chubby, goofy, socially-isolated, sensitive kid getting bullied in America who feels like no one in the world cares about them.” In recent years, Martin has spoken to schoolchildren about his experiences with bullying and depression on behalf of Beyond Differences.

Martin’s disturbing Instagram post comes a week after 17 people were killed in a mass shooting at Stoneman Douglas High School in Parkland, Fla., just 33 miles from the home of the Miami Dolphins.

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Ben Rohrbach is a writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach