A New York City police officer is among four people killed after a gunman opened fire in a Midtown Manhattan office tower on Monday evening, before turning the weapon on himself.

The attacker, identified by police as 27-year-old Shane Devon Tamura from Las Vegas, entered the high-rise at 345 Park Avenue around 6:30 PM ET armed with what authorities described as an MR rifle, clearly visible as he walked through the lobby. Without warning, he began firing indiscriminately, first in the lobby and later on an upper floor.

The shooting unfolded in one of the busiest districts of the nation’s largest city, sending nearby pedestrians scrambling for safety as law enforcement warned of an active shooter.

Inside the building, terrified employees barricaded themselves inside offices, using furniture to block doors as gunfire echoed through the halls.

Authorities say Officer Didarul Islam, a three-year veteran of the NYPD who was working a security detail at the time, was fatally shot at the building's entrance.

Islam, originally from Bangladesh, leaves behind a pregnant wife and two children. NYPD Commissioner Jessica Tisch praised him as a hero, saying, “He died doing what we ask of all our officers protecting others.”

According to investigators, Tamura moved through the lobby, firing at random. He shot a woman attempting to take cover behind a pillar, a man near the reception area, and another security guard hiding behind a desk.

Moments later, as he waited for the elevator, a woman exited but Tamura reportedly let her pass without harm.

Upon reaching the 33rd floor, home to Ruden Building Management, the gunman opened fire again, killing another person before walking down the corridor and fatally shooting himself.

While the motive remains unknown, police say Tamura had a documented history of mental health issues.

Investigators also revealed he had driven across the country in recent days, making stops in Colorado, Nebraska, Iowa, and New Jersey before arriving in New York shortly before the attack. It’s unclear whether he had any personal or professional connection to the building or its tenants.

Outside the building, Tamura had left his BMW double-parked. Inside, police recovered a revolver and several magazines. The car, registered in Nevada, confirmed his identity and gun ownership status.

The aftermath of the shooting brought a major section of Midtown Manhattan to a standstill. Subway stations and streets were temporarily shut down as heavily armed officers swept the building room by room a process that stretched into the night.

A BBC journalist on the scene reported seeing a person with a chest wound taken away on a stretcher.

Nearby, employees from surrounding buildings were seen being evacuated with their hands raised. Mama Bouhenni, a barista at a local coffee shop, told the BBC she recognized many of them as regular customers.

“It was terrifying,” she said. “I just hope everyone gets home safely.”

The three other victims have not yet been named as next of kin are notified.