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.

Once a promising athlete, the 27-year-old faded from public view—until he showed up at 345 Park Avenue, gun in hand.