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.

There were 23 shell casings and 13 bullet fragments recovered from the lobby of 345 Park Avenue and 24 spent shell casings on the 33rd floor, police said.

A man stalked through a Manhattan office tower firing a rifle, killing four people, including a New York City police officer, and wounding a fifth before taking his own life, officials said.