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.

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.

The alarm reached Jon Gray on the 44th floor, in his C-suite office high above Park Avenue: An active shooter was in the building.In the lobby below, a gunman had opened fire, killing a uniformed police officer and two others who worked in the office tower.

Five people were shot and four killed by the 27-year-old gunman Shane Tamura, when he opened fire inside an office building at 345 Park Ave. on Monday evening. Among the victims were a Police Officer,

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.

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.

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.

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.

NFL commissioner Roger Goodell released an internal memo to NFL employees amid the acts of the Park Avenue shooter Monday. Goodell also revealed an NFL employee was among those seriously injured in the attack.