It was not immediately clear whether Martin posted the photo himself and he was not under arrest Friday afternoon.
"According to Martin, in middle school and high school he was the victim of bullying, which diminished his self-confidence and self-esteem and contributed to what he self-diagnosed as periodic bouts of depression during his teenage years", the report said.
The shooting reignited a nationwide conversation about gun violence and school safety, as the survivors of the shooting have launched a nationwide campaign calling on lawmakers to respond to the violence.
Martin, who is bi-racial, also had complained of feeling unaccepted at Harvard Westlake, an elite private school with campuses in Holmby Hills and Studio City, and on the affluent Westside of Los Angeles, where he moved at the age of 10.
LOS ANGELES-Former Miami Dolphins offensive lineman Jonathan Martin, who has struggled with mental health issues after a 2013 bullying scandal that shook the National Football League, was questioned by Los Angeles police after a threatening Instagram post on his account mentioned two former teammates who had harassed him.
The closure of the private high school was announced in message sent out to parents on the school's emergency notification system Friday morning, in what officials termed a "security threat". Authorities said the post mentioned Harvard-Westlake School by name.
The threat was taken as a serious threat by his former high-school which went on lock-down shortly after the post was made on Instagram. Martin is Black and Incognito is white. "We will provide more information later today". Martin was briefly claimed by the Carolina Panthers, but sat out the 2015 season due to a back injury which ultimately ended his playing career.