Firefighters first discovered the 32-year-old mother stabbed to death while battling flames inside the Albany Crescent apartment in the Kingsbridge section. Police say she was found on her bed under a burning mattress.
The woman's 1-month-old baby girl was pulled from the fire and rushed to Montefiore Medical Center, but she later died at the hospital. NYPD Commissioner Ray Kelly said the child was not stabbed.
Officials say the fire was reported just after 7 p.m. Thursday and was brought under control about a half hour later.
Police believe the fire was set in the apartment to cover up the murder.
The girl's biological father is being questioned at the 50th Precinct in the Bronx. No charges were immediately filed.
The father, believed to be the woman's boyfriend, lived with her until recently.
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