Former NFL player Jonathan Martin, who became more widely known after speaking out about being bullied by members of the Miami Dolphins, has reportedly been detained by police after he allegedly posted a photo of a gun, ammunition and the names of former NFL players.

TMZ reports that the post initially appeared on Martin’s Instagram account and showed an image of a shotgun surrounded by ammunition with the caption, “When you’re a bully victim & a coward your options are suicide, or revenge.”

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Martin also posted the social media handles for ex-Dolphins teammates Richie Incognito and Mike Pouncey. He also listed his former high school, Harvard Westlake, in his post. The school closed amid the threats, with administrators telling students to stay off campus as a precaution.

“The individual we believe to be responsible for the social media post has been detained and the investigation is ongoing,” officials told TMZ.