Twelve years after moving to the United States from Bangladesh, Didarul Islam sought to join the ranks of the nation's largest police department because he "got inspired" by the "blanket" of protection the NYPD provided to his community, according to an essay he wrote as part of his police academy application.

Investigators are examining why the gunman who killed four people before taking his own life at a New York City office tower targeted the National Football League and whether he suffered from a brain disease.

A New York City police officer and three other people were killed in a shooting in Midtown Manhattan on Monday evening, police confirmed at a late-night news conference.