They also ruled out that the fire was caused during an arson in the house.
Twenty suspects have taken into custody for negligence causing serious accident, official media reported.
The fire engulfed a three-story apartment building, mostly inhabited by migrant workers, in Xinjian village in Beijing's southern Daxing district on November 18.
Following the incident, authorities started evacuating thousands of migrant workers in the name of safety which caused unrest among the people.