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.

Police lined the streets of New York City to pay their respects to fellow officer Didarul Islam, who was among the four victims of a gunman’s rampage Monday at a Manhattan office tower.

Family, friends, and colleagues of slain NYPD officer Didarul Islam gathered at Parkchester Jame Masjid Mosque in the Bronx for his funeral.