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 who was among the four people shot and killed by a gunman during a rampage at a Manhattan office tower will be laid to rest Thursday. Officer Didarul Islam, 36, was fatally shot Monday in a midtown building housing the National Football League’s headquarters.

Politicians, relatives and members of the New York City Police Department are gathered at the funeral for the "hero" officer who was one of four people killed in the Midtown Manhattan mass shooting. Didarul Islam,