A gunman killed at least four people at a Manhattan office building on Monday evening, the AP reports, one of them an off-duty New York City police officer shot while exchanging fire with the shooter in the lobby, NBC News reports. The suspect then disappeared into the skyscraper, and panicked employees ran into the streets screaming. Police said they later found the gunman on the building's 33rd floor, dead of a self-inflicted gunshot wound, and they described him as a 27-year-old man from Nevada who acted alone. The Park Avenue building houses the offices of some of major financial firms, per the AP, as well as the National Football League.