The glittering skyscraper where hundreds work became the scene of New York City’s deadliest gun attack in 25 years when a man entered the lobby and started shooting.

NEW YORK (Reuters) -A spokesman for audit and advisory firm KPMG said in a statement the office at 345 Park Avenue will be closed on Tuesday, after a shooting in the building on Monday evening that left four dead, including a Blackstone executive.

A 27-year-old man wearing body armor and carrying an M4 assault rifle shot and killed four people, including an off-duty police officer working security in a Midtown Manhattan office building, officials said during a press conference Monday evening.

Julia Hyman, 27, was working late when the gunman fired into the office where she worked, which, it appears, was not his intended target.

The deadly Park Avenue shooting happened at one of the the most exclusive addresses in Midtown Manhattan — the “Blackstone Building," which is home to financial giant Blackstone, the NFL and accounting firm KPMG among a slew of other corporate names.

Shane Tamura, the Park Ave. gunman who killed an NYPD officer and three others before taking his own life, left behind a suicide note saying he suffered from CTE, a brain injury often linked to playing football, police sources said Tuesday.

Four people were killed and a fifth was injured in the mass shooting at a Midtown Manhattan office building on Monday.

A suspect was spotted entering the Blackstone building holding an assault weapon. Get updates on the developing situation.

Nearly 24 hours after a deadly Midtown mass shooting that left four people dead, including an off-duty police officer, detectives from the NYPD Crime Scene Unit combed through the plaza outside 345 Park Ave.