NEW YORK (CBSNewYork) — When residents of a building on Fort Hamilton Parkway in Borough Park smelled gas Saturday, they immediately called 911 and firefighters evacuated all 20 apartments.

But inside one apartment, they found the body of a 55-year-old woman, CBS2’s Matt Kozar reports.

“I called and called and rang the doorbell and nobody opened,” explained Jimmy Marquez.

When his sister didn’t answer the door to their first floor apartment, Marquez knew something was wrong. He says he found her body on the first floor.

“I just saw her lying there,” Marquez said. “I gave her CPR and I touched her, and I tried to revive her and I couldn’t.”

Nilda Sing, 55, was pronounced dead at the scene.

It happened Saturday morning as firefighters evacuated this apartment building on Fort Hamilton Parkway in Borough Park because of high carbon monoxide levels.

National grid confirms the gas leak came from the building’s boiler.

Marquez says his apartment is directly above the boiler.

“The past few weeks they were working on the boiler and finally they got it to work.”

Ayda Yousef, who has two kids, says this is not the first time there’s been a gas leak inside the building.

“I’m looking for another apartment,” Yousef said. “I want to move. I’m scared for myself and my kids.”

The medical examiner has yet to determine how sing died, Kozar reports. Her brother says she had diabetes and other health issues.

CBS2 reached out to the building owner but have not heard back for comment.