Sebije Nelovic had just taken out the trash from one conference room and was heading into another when she heard the first loud pops echo down the hallway.

“I said, ‘What’s going on? Firecrackers?’,” she told Bloomberg News on Thursday.

It wouldn’t have been strange to hear the engineers who worked upstairs moving around. They wore heavy boots and sometimes came down in groups, talking and joking.

But then the door shook. And then it shattered.

“I saw the glass fall — boom,” she said. In the middle of the floor stood a man with an assault rifle. “He put it up, straight at me. Oh, my God. God help me.”

Nelovic, a cleaner at Rudin Management for 27 years, turned and ran. She darted through the hallway, past the elevators and stairs and into a private bathroom where she hid in a closet.

Outside the door, the violence continued.

On Monday evening, just before 6:30 p.m., Shane Tamura stepped out of a black BMW outside 345 Park Avenue with a fully assembled AR-15–style rifle. He calmly walked into the building and began firing in the lobby.

First, he shot and killed Didarul Islam, an NYPD officer working for the building’s security detail. He then shot and fatally wounded security guard Aland Etienne. Wesley LePatner, a senior managing director at Blackstone Inc., was also killed in the lobby. Craig Clementi, an employee in the NFL’s finance department, was shot and survived.

Read more: Blackstone Real Estate Star LePatner Killed in NYC Shooting

Investigators believe Tamura was targeting the NFL’s offices, but took the wrong elevator bank and instead arrived at Rudin Management on the 33rd floor, where Nelovic was working. There, he fired through a glass wall, stepped forward, and opened fire.

Nelovic, from her hiding place inside the bathroom, could hear it all.

“I heard one shot,” she said. “Then I hear somebody scream. And I said, oh my God, oh my God, oh my God.”

She started worrying about Julia Hyman, a Rudin associate who often worked late and who she saw most nights while cleaning.

“She’s sweet,” Nelovic said of Hyman, 27, who she later found out had also been killed in the attack. “She was sweet.”

When police arrived they found Tamura dead at the scene. He had turned the rifle on himself.

Nelovic stayed quiet in the closet until officers arrived and opened the door. One of them helped her downstairs.

“He told me, ‘You’re gonna be OK,’” she said. But what she saw in the lobby — the blood, the aftermath — left her shaken. “I’m not gonna forget,” she said. “Never.”

She’s not sure if she’ll return — to the building, where she’s worked for almost three decades, and to Rudin Management, the family-run real estate company whose owners she considers “like my family.”

“It’s scary to go to work,” she said.