Police have identified the man who entered a Midtown Manhattan office building wearing body armor and opened fire killing four people with a high-powered rifle.

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.

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,