The remains were found inside the Buchanan Place building on Monday afternoon.
FDNY Fire Marshals said on Wednesday that the fire at 61 Buchanan Place was accidental, caused by an unattended candle in the basement.
A spokesman says a man seen leaving the home on surveillance video prior to the fire was a squatter.
Neighbors on the street say it was well-known that at least four squatters were living in the home for some time.
"They lived there. They came in day and night. It was there home," Felix Santora said.
Several residents say they made this known to firefighters at the scene.
"That there were squatters living in the building going in and out of the building," Maxine White said.
The FDNY says they believed the building was vacant and that there was no indication anyone was inside. Their search was limited, they say because they feared structural collapse. On Monday, 7 days after the fire, a demolition crew found three bodies on the second floor. But city Buildings Department records show the FDNY knew of an on-going squatter problem at the home. Some residents say the FDNY failed to complete their job.
"There was negligence on part of the firefighters cause they just put fire out and left and never came back to check to see if bodies were there," Jose Pagan said.
The investigation continues into why it took seven days for the bodies to be found.