Four people were killed, including an off-duty New York City police officer, when a gunman opened fire in an office tower before fatally shooting himself, officials said.

Barriers were erected in front of the ritzy Midtown Manhattan office building where a crazed gunman killed four people Monday, with access being restricted even to some who work there.

NYPD officials are heading to Las Vegas to investigate the gunman who killed four people in a Midtown Manhattan skyscraper.

The police officer who was killed when a gunman opened fire in a Manhattan building was a dedicated father who was working a second job as a security guard.

A shooting at a midtown Manhattan office building on Monday left at least five people dead, including an off-duty New York City police officer, sources told The .

A note written by the shooting suspect was found at the midtown Manhattan office building scene where he killed four people, including an NYPD officer, and himself a day ago, officials familiar with the investigation said overnight.