Joanna Mei is charged with two counts of murder and two counts of arson. She is believed to have an ongoing disagreement with a neighbor who leaves her property in the hallway.
The flames broke out inside an apartment on 11th Avenue in Dyker Heights just after 7 a.m. on Thursday.
More than 100 firefighters and EMS personnel battled the heavy smoke and flames.
First responders discovered a 58-year-old man, identified as Xi Huang, and a 56-year-old woman, identified as Feng Xu, unresponsive on the third floor. They were both pronounced dead on the scene.
Officials say another family that included a 4-year-old girl and a 3-month-old boy, were rushed to Maimonides Hospital in stable condition to be treated for smoke inhalation.
Three firefighters were also injured during the blaze, with one of them suffering minor burns.
Authorities say Mei made statements indicating she set fire to the materials left in the hallway. She is believed to have used accelerant that she had in her possession.
The woman has a history of mental health issues, officials said.
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