Although there's a chance that Martin's verified page was hacked, the threat was serious enough that police in Los Angeles chose to shut down Harvard-Westlake on Friday due to the serious nature of the photo and due to the recent shooting attack at a high school Parkland, Florida, that left 17 dead.
A source who had access to the picture said: 'This seems like a joke gone horribly awful wrong'.
Martin became the victimized face of National Football League bullying in 2013 when he charged teammates, namely fellow offensive lineman Richie Incognito, with harsh treatment in the locker room.
The current Buffalo Bills player also joked about "running a train" on Martin's sister, and made other crude remarks about her.
He ultimately quit the team and debated giving up on his career, feeling such psychological duress that he said he twice considered committing suicide. Both reports linked the closings to the post on Martin's account.
Harvard-Westlake high school also released a statement to explain why the school was closed on Friday.
Jonathan Martin, the former Miami Dolphins offensive lineman who accused Richie Incognito and Mike Pouncey of bullying during his time on the team, posted the above disturbing image to Instagram Story, according to those who saw it Thursday night.
The decision to close the campuses Friday was made by school officials, not police, Kuey said.
"Last evening, we learned an Internet post that mentions Harvard-Westlake by name".
Law enforcement tells TMZ Sports. Kate Beckinsale's children now attend the school.
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.
The incident comes a little over two weeks after 17 students and staff were shot to death at Marjory Stoneman Douglas High School in Parkland, Fla.