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.

Follow along for live updates on the New York City shooting, where police investigate motive after five people, including the gunman, were killed in the Monday shooting.

Police lined up four rows deep in front of a mosque on Thursday to pay respects to a fellow officer who was among the victims of a gunman's rampage at a New York City office tower. Fire trucks bore a huge American flag down the street ahead of services for Officer Didarul Islam,