The fire apparently broke out on the first floor in back of the two-story Spruce Street building and instantly spread to the second floor and a cockloft -- trapping the victims -- shortly before 9:30 a.m. March 3.
A vehicle just outside the brick structure also caught fire.
A battalion chief reported heavy fire and smoke right from the get-go.
The adult victims' bodies were found soon after, Passaic Mayor Hector Carlos Lora said. They were pronounced dead at the scene.
Firefighters had the three-alarm blaze under control within two hours.
Mutual aid included firefighters from Carlstadt, Clifton, East Rutherford, Paterson, West Paterson and Wallington.
The North Jersey Fire Canteen Support Unit also responded.
Passaic and Passaic County prosecutor's investigators were trying to determine the cause.
Damien Danis took the photos and contributed to this story.
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