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.

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.

The cases are most likely linked to a cooling tower in central Harlem, health officials said. At least 22 people have fallen ill, including one person who has died, from Legionnaires’ disease in New York City over the last two weeks, according to the city’s health department.

New York City officials said they are investigating a cluster of Legionnaires' disease that has caused one death and nearly two dozen illnesses.