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.

Investigators are combing through evidence in the wake of New York City’s deadliest mass shooting since 2000, trying to figure out more about the gunman who unleashed an assault-style rifle in Midtown,