A former Miami Dolphins player was behind a sinister social media post threatening a shooting that led to his old high school being evacuated and him being taken into custody on Friday, sources tell DailyMail.com.

Troubled Jonathan Martin, 28, posted a picture on his private Instagram feed late on Thursday of a shotgun and cartridges on a bed, with the caption: "When you're a bully victim & a coward, your options are suicide, or revenge."

In the chilling post, he hashtagged his former school, Harvard-Westlake in California and the Miami Dolphins, reports Daily Mail.

Harvard-Westlake School, an elite private school costing $38,000 a year and popular with celebrities, was forced to close its Studio City campus after one of its students highlighted the post as a possible "security threat" on social media, police said.

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Los Angeles Police Department Officer Tony Kuey said the former student, who is now an adult, made no direct threat against the school.

One source at Harvard-Westlake said Martin has been detained over the incident, though police said there was "no credible threat" against students.

A spokesperson for LAPD told DailyMail.com: "There was a post on social media and for precautionary measures they added extra patrols to the school."

Troubled Martin, 28, posted this picture on his private Instagram feed late on Thursday night. Photo / Instagram
Troubled Martin, 28, posted this picture on his private Instagram feed late on Thursday night. Photo / Instagram

The spokesperson was unable to confirm Martin's involvement and said they had no information about there suspect or a possible arrest.

But sources said the social media post came from the private Instagram account of former NFL player Martin, who is known to suffer from a depressive disorder.

A source who had access to the picture said: "This seems like a joke gone horribly horrible wrong."

Stanford University graduate Martin was a player for the Miami Dolphins, but left in 2013 amid allegations he was a victim of racist bullying.

Martin's chilling Instagram post tagged the name of former Dolphins player Richie Incognito. Photo / Getty
Martin's chilling Instagram post tagged the name of former Dolphins player Richie Incognito. Photo / Getty

Martin's teammate Richie Incognito was investigated by the NFL Players Association over allegations that he was the ringleader of a group of Dolphins players who bullied Martin for months.

Incognito left voicemails on Martin's phone calling him a "half-n****r piece of s**t", threatening to slap his mother and even making death threats against Martin.

The current Buffalo Bills player also joked about "running a train" on Martin's sister, and made other crude remarks about her.

Martin, who played offensive tackle for the Dolphins, reportedly checked into a hospital for emotional distress over the incident, and returned to his parents home in California.

The tag also included current Dolphins player Mike Pouncey. Photo / Getty
The tag also included current Dolphins player Mike Pouncey. Photo / Getty

He ultimately quit the team and debated giving up on his career, feeling such psychological duress that he said he twice considered committing suicide.

In November that year, Incognito was suspended for "conduct detrimental to the team."

Martin's chilling Instagram post tags the names of Incognito and another Dolphins player Mike Pouncey above the shotgun.

Also tagged in the Instagram post was sports agent James Dunleavy, VP Basketball at Independent Sports & Entertainment and TJ Taylor, a top executive at an exclusive dating app - both appear to be former students at Harvard-Westlake.

It's not clear whether Martin also suffered from bullying at Harvard-Westlake.

Martin ultimately quit the team and debated giving up on his career, feeling such psychological duress that he said he twice considered committing suicide. Photo / Getty
Martin ultimately quit the team and debated giving up on his career, feeling such psychological duress that he said he twice considered committing suicide. Photo / Getty

Police have stationed extra patrols around the area of the Harvard-Westlake campus, and school officials chose to close the campus on Friday.

The school's campuses in Los Angeles are expected to remain open.

The school sent out an alert to parents at 7am on Friday saying that the Studio City campus had been closed due to a "security risk".

"We apologize for the short notice; the safety of our students is our highest priority," the alert said.

The school later issued a statement saying: "Last evening, we learned of an Internet post that mentions Harvard-Westlake by name. Out of an 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."

Harvard-Westlake School, which is popular with celebrities, was forced to close its Studio City campus. Photo / Getty
Harvard-Westlake School, which is popular with celebrities, was forced to close its Studio City campus. Photo / Getty

"We are working closely with law enforcement and will share more information when we are able."

Harvard-Westlake celebrity alumni include Jake and Maggie Gyllenhaal and Shirley Temple. Kate Beckinsale's children currently attend the school.

Matt Yam, 18, an editor at the school's student newspaper, told the LA Times: "Honestly it's not bad. Everybody is calm, a lot of people are leaving now, everything is under control... People don't seem too worried."

In recent years troubled Martin received a degree from Stanford and had been working with Beyond Differences, an organization focused on eliminating social isolation, and had given talks to schoolchildren.

In 2016 he gave a talk to 7th graders. at Washington Manor Middle School in which he said: "I was trapped in my own head often, and I would later learn that I have major depressive disorder, which means you get sad easier than other people, and I get anxiety to go along with that."