The New York City office building that was the scene of a shooting on Monday night that left four victims dead, including an NYPD officer, serves as the headquarters for several firms in the financial services industry as well as the NFL.

Monday night's shooting was at 345 Park Avenue in midtown Manhattan, which is the headquarters of alternative investment firm Blackstone, real estate firm Rudin Management and the National Football League (NFL). 

The building is owned by Rudin Management and is also home to an office for multinational accounting firm KPMG. 

The skyscraper was constructed on the site of the former Hotel Ambassador, with construction completed in 1969. Blackstone is a longtime tenant and first moved into the building in 1988, just three years after its founding, and last year moved to expand its presence in the facility.

Blackstone inked a deal last year that increased the footprint of its office space lease from 719,000 square feet to 1.06 million square feet, giving the firm 55% of the building on 28 floors, according to a report at the time by CoStar News. 

The firm's original 1988 lease spanned just two floors and 70,000 square feet, while the new lease runs through 2034.

Rudin Management traces its roots to a family real estate venture in the early 1900s, which over time grew into a real estate development firm that built high-rise apartments and office buildings in New York City. The 345 Park Avenue building was its first commercial office building, according to the company's website.

Mayor Eric Adams appeared on Fox 5 NY's "Good Day New York" and said that the gunman, who has been identified as Shane Tamura, accidentally entered the wrong elevator banks.

"It's unfortunate that during these days and times, active shooter drills are taking place all across the country and Rudin Management did their job of clearly having those active shooter drills and the staffers who were in the building were able to utilize some of the safe rooms and I believe it played a great role in saving lives of some of the staffers," Adams said.

Adams added that the gunman alluded to having suffered from chronic traumatic encephalopathy (CTE) and had a grievance against the NFL, adding that investigators were going through a "suicide note" left by the gunman. The New York Post first reported on the note found near the gunman's body.

NYPD Commissioner Jessica Tisch said Monday night that Tamura "has a documented mental health history" and traveled by car across the country to the city. She explained that his motives are still under investigation.

Blackstone identified one of the victims as Wesley LePatner in a statement. LePatner served as Global Head of Core+ Real Estate and the CEO of Blackstone Real Estate Income Trust (BREIT), according to the company's website.

The NYPD identified Didarul Islam as the slain police officer. The NFL said that one of its employees was "seriously injured" in the attack.

The New York Post reported that Rudin associate Julia Hyman was killed in the shooting.

The New York Times reported that Blackstone's offices in Manhattan will be closed on Tuesday in the wake of the shooting, according to a person familiar with the matter who wasn't authorized to speak publicly.

KPMG said in a memo to employees that was reported by Business Insider that its office will be closed on Tuesday following the shooting, and they should work from home or another office.

Fox News Digital's Anders Hagstrom and Ryan Gaydos contributed to this report.