Police and fire investigators are combing through the rubble of a Bed-Stuy fire that may have been set to cover-up a woman's murder Monday.

Authorities say the fire broke out around 1 a.m. at 39 Rochester Ave. Responders say they arrived to find 31-year-old Wanett Douglas with stab wounds and her 5-year-old daughter suffering from smoke inhalation. Both were transported to Kings County Hospital; the daughter survived, but the mother died.

The fire completely gutted the second floor of the home. Neighbors alerted police about the blaze. "All we heard was a big bang upstairs and we ... banged on the door. She didn't open," neighbor D.J. Niare said.

Neighbors describe Douglas as a hard-working MTA employee.

Fire marshals say it could take days to determine the cause of the suspicious fire.