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 shooting at a Manhattan office building left at least five people dead, sources tell the The Associated Press.

At least two people, including a New York City police officer, have been shot in a Manhattan office building, a person familiar with the matter tells The Associated Press. The person did not immediately know their conditions. The person was not authorized to publicly discuss the ongoing investigation and spoke to AP on condition of anonymity.