Four people were killed when a gunman stormed into a New York City skyscraper at the end of the business day on Monday. 

An off-duty New York City Police Department (NYPD) officer, a security guard, a Blackstone executive and a Rudin employee were fatally wounded at 345 Park Avenue at 52nd Street in Midtown Manhattan.

Authorities said Monday night that a fifth victim had been shot and was hospitalized in critical but stable condition. 

The accused gunman – identified as 27-year-old Shane Tamura – died of a self-inflicted gunshot wound on the 33rd floor of the building, according to police. 

The building houses offices for the Blackstone Group, the National Football League (NFL), Rudin Management Company and "Big Four" accounting firm KPMG, among other businesses. The motive remains under investigation. 

Authorities said Tamura was a Las Vegas resident who last worked an overnight security job at Horseshoe Las Vegas. New York City Mayor Eric Adams told Fox News that NYPD teams are traveling to Las Vegas to conduct a search warrant on Tamura's home and determine how Tamura obtained the AR-15-style rifle used in the shooting. Investigators believe Tamura assembled the gun using a lower receiver purchased by "an associate." 

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The NYPD identified Officer Didarul Islam as among those killed. Islam, 33, of the Bronx, was an immigrant from Bangladesh who worked in the NYPD's 47th Precinct, according to Adams. 

Islam, who served in the NYPD for about three and a half years, was off-duty at the time of the shooting and was working as a private security guard at the building. His wife is pregnant, soon to give birth to their third child.

In a video statement Tuesday, NYPD Commissioner Jessica Tisch said "in an act of senseless violence, we lost a brother, a friend, and an NYPD hero." 

Islam "was murdered, wearing the uniform respected the world over. Your uniform," she told the force. "Officer Islam's death was yet another reminder of everything you risk just by showing up to work. He knew that risk. He embraced it. He understood what it meant to put the safety of others above his own. Now, we owe it to him and every member of this department to sift through the chaos of yesterday's crime scene and get some answers." 

NYPD officers lined the streets on Monday night as they carried out a dignified transfer of Islam's body. 

Islam "put on his uniform and went to work. To protect his city," the Police Benevolent Association of the City of New York wrote on X. "To provide for his family. He should have been going home to them tonight."

"Instead, we are carrying him on his final journey," the union added, asking for prayers for the victims and their families. "And please pray for the police officers who will carry on protecting this city from the evil we saw tonight."

New York City hosted a multi-faith vigil and prayer service in Bryant Park on Tuesday night to honor the victims. 

Blackstone mourned 43-year-old Wesley LePatner as "a beloved member of the Blackstone family" who "will be sorely missed." 

She joined the company in 2014 after a decade-long career at Goldman Sachs. A highly-regarded senior executive, she served as Blackstone's Global Head of Core+ Real Estate and the CEO of the Blackstone Real Estate Income Trust (BREIT). 

LePatner took over as BREIT CEO on Jan. 1 of this year. The $53 billion real estate fund caters to wealthy clients. 

"She was brilliant, passionate, warm, generous, and deeply respected within our firm and beyond. She embodied the best of Blackstone," Blackstone said in a statement. "Our prayers are with her husband, children and family. We are also saddened by the loss of the other innocent victims as well, including brave security personnel and NYPD."

LePatner, a married mother of two children, was also an active member of the Park East Synagogue in Manhattan. 

The UJA-Federation of New York, a charitable organization supporting Jewish communities, said LePatner led a "solidarity mission" with UJA to Israel in the wake of the Oct. 7, 2023, attacks by Hamas, "demonstrating her enduring commitment in Israel's moment of heartache." The organization said she "lived with courage and conviction, instilling in her two children a deep love for Judaism and the Jewish people." 

"We are all mourning the loss of such an extraordinary person and extend our heartfelt condolences to her entire family," UJA added. 

LePatner met her husband, Evan LePatner, during their freshman year at Yale University. He is a managing partner at the private equity firm Courizon Partners. 

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The Service Employees International Union (SEIU) identified one of its members, Aland Etienne, as one of the shooting victims killed. The union remembered Etienne as "a dedicated security officer who took his job duties extremely seriously." 

"We have been in touch with Aland Etienne’s family and are working with building management and the NYPD to support their investigation," 32BJ SEIU, which is the largest property service workers' union in the country, said in a statement. "We are ensuring our members in the building receive the free union counseling and support services they deserve and need to manage this unspeakable loss." 

"This tragedy speaks to the sacrifice of security officers who risk their lives every day to keep New Yorkers and our buildings safe," the union added. "Every time a security officer puts on their uniform, they put their lives on the line. Their contributions to our city are essential, though often unappreciated. Aland Etienne is a New York hero. We will remember him as such." 

Etienne’s brother, Gathmand Etienne, also released a statement on social media. 

"My family suffered a heartbreaking tragedy. My brother, Aland, lost his life in the shooting that happened in New York while he was at work," he wrote on Facebook. "He was more than a brother – he was a father, a son, and a light in our lives. Our hearts are shattered, and we’re asking for your prayers and strength as we navigate this painful time."

"Rest in peace, Brother. You’ll never be forgotten," he added. 

Rudin Management Company said that one of its employees – reportedly a graduate of Cornell University just five years out of college – was killed in the shooting. Her family has asked for privacy. 

"The Rudin family and everyone at our company are devastated by yesterday's senseless tragedy. Our thoughts and prayers are with those injured and lost last night, including our cherished Rudin colleague, a brave New York City police officer, a beloved lobby security guard and an employee at a tenant firm," the company said in a statement. "We are grateful to the NYPD, FBI, EMS and multiple other emergency responders for their swift and courageous action."

The company also thanked the mayor and the police commissioner for "their leadership" and said the building would remain closed Tuesday as the authorities continue their investigations. 

"As New Yorkers, we stand shoulder to shoulder in the face of this hatred, we grieve with the families and loved ones of those lost, and we pray for the full recovery of those injured," Rudin added. 

At a press conference Monday, the NYPD commissioner detailed how multiple 911 calls came in at approximately 6:28 p.m. to report an active shooter inside 345 Park Avenue. 

Tamura exited a double-parked black BMW with Nevada plates on Park Avenue between 51st and 52nd streets, carrying an M4 rifle in his right hand, Tisch said. The building's security camera footage showed the gunman enter the lobby, turn right, and immediately open fire on an NYPD officer. He then shot a woman who took cover behind a pillar and proceeded through the lobby, spraying it with gunfire, according to the police commissioner. 

Video shows him making his way to the elevator bank, where he shot a security guard who was taking cover behind a security desk, police said. Tisch said an additional male – the hospitalized survivor – was shot in the lobby. 

Police said the shooter then called the elevator, which opens in the lobby. "A female exited that elevator, and he allowed her to walk past him unharmed," Tisch said. 

The shooter then went to the 33rd floor, where Rudin Management is located, and began to walk around and fire rounds. One person was struck and killed on that floor, police said. 

Tisch said the gunman proceeded down a hallway and shot himself in the chest. 

Investigators believe Tamura's vehicle traveled cross-country through Colorado on July 26, then through Nebraska and Iowa on July 27. The vehicle was spotted in Columbia, New Jersey, around 4:24 p.m. Monday before it entered New York City. 

Tisch said law enforcement partners in Las Vegas reported that Tamura had "a documented mental health history." 

Adams said investigators were analyzing a suicide note in which Tamura expressed his belief that he experienced chronic traumatic encephalopathy, or C.T.E., and voiced grievances with the NFL.

Tisch said the gunman allegedly wrote "study my brain" in the note. Adams said that Tamura likely wanted to target the NFL office but took the wrong elevator bank. Tamura played football in high school in Los Angeles County but never in the NFL. 

Fox News' Brooke Taylor, Leonard Balducci and Terrence Kenny contributed to this report.