(CNN) A former NFL player who attended a prestigious private high school in Los Angeles was detained by police Friday in connection with a social media post that prompted the closure of the school due to security concerns, according to two law enforcement sources familiar with the matter.

Jonathan Martin, who graduated from Harvard-Westlake in 2008 and went on to play as an offensive lineman for the Miami Dolphins and San Francisco 49ers, was being questioned by LAPD detectives about the post, the sources confirmed. The sources requested not to be named due to the sensitive nature of the ongoing investigation.

The image in question depicted a black shotgun with the words #HarvardWestlake superimposed over it and shotgun shells scattered around the weapon.

There was also a reference to "#MiamiDolphins" on the gun. A message to the side of the weapon read: "When you're a bully victim & a coward, your options are suicide or revenge"

The image was circulated among students at Harvard-Westlake and was shared with CNN. School officials said the image had been attributed to a former student, but did not identify the person.

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