The gunman suspected of targeting the National Football League headquarters in New York, killing four, was a former football player at two Southern California high schools.

Police have identified the man who they say entered a Midtown Manhattan office building wearing body armor and opened fire, killing four people with a high-powered rifle, as Shane Devon Tamura.

The gunman, who said in a note he believed he had CTE, targeted skyscraper that houses the NFL's headquarters.