A female off-duty NYPD officer was among four people fatally shot Monday evening after a gunman armed with a rifle and clad in body armor opened fire inside 345 Park Avenue, an office building that houses Blackstone and the NFL's headquarters, according to multiple law enforcement officials. The suspect was later found dead from a self-inflicted gunshot wound on the 33rd floor.

The gunfire erupted shortly before 6:30 p.m. in Midtown Manhattan, prompting a massive law enforcement response and lockdowns across the building. NYPD Commissioner Jessica Tisch confirmed on X that the "lone shooter has been neutralized."

At least five individuals were shot in total. Three civilians died, and a fifth victim remains in critical condition at Bellevue Hospital. The off-duty officer, working a security detail at the site, was transported to Weill Cornell Medical Center, where she was pronounced dead.

The identity of the shooter has not been released. Surveillance footage showed the gunman wearing sunglasses and wielding what appeared to be a long rifle as he entered the building's lobby.

Officials said the shooter began firing in the lobby, moved through multiple floors, and ultimately took his own life on the 33rd floor. Investigators are working to determine whether he had a specific target or ended up there incidentally.

During the attack, employees sought cover in offices, kitchens, and bathrooms. Jessica Chen, an employee in the building, described the fear and confusion. "The only thing between me and the door was a chair flipped over," she told ABC News. "I texted my parents 'I love them.' Nothing can describe that feeling."

NYPD and FBI agents, along with personnel from the New York Sheriff's Department, secured the scene floor by floor. Law enforcement sources confirmed no second shooter was found after a full sweep of the premises.

Mayor Eric Adams urged New Yorkers to avoid the area around East 52nd Street between Park Avenue and Lexington Avenue. "Please take proper safety precautions if you are in vicinity and do not go outside if you are near Park Avenue and East 51st Street," he posted on X.

Emergency notifications warned of major disruptions to local traffic and transit. Attorney General Letitia James posted that she was "praying for our law enforcement and the New Yorkers impacted." FBI Deputy Director Dan Bongino confirmed that the agency was assisting the NYPD, which retains lead jurisdiction in the investigation.