The Nov. 24 fire engulfed the Tazreen Fashions Limited facility on the outskirts of capital Dhaka when more than 1,100 workers were in the nine-story building.
"It was an act of sabotage," Main Uddin Khandaker, who headed the investigation, told The Daily Star via telephone. He said his team has recommended legal action against the factory owner and nine mid-level managers for the deaths due to their negligence, the report said.
"We have analyzed developments of the fire incident chronologically. We have spoken to the witnesses, examined the place and also taken assistance from experts," Khandaker said.
"There was no possibility of fire originating from an electric short-circuit, as there was no electric wire near the place," he said, the Star reported. "It came from outside. The accounts of witnesses and the factory workers who escaped the fire also revealed that it was an act of sabotage."
It was, however, not clear who might have been responsible for starting the fire or the motive behind such an act.
The government said a more detailed probe has been recommended to identify those responsible for the fire.
CNN reported more than 200 people also were injured in the blaze.
CNN said the factory owner could not be reached for comment but that he had earlier told local media the factory lacked proper safety measures although he had not been aware of it.
CNN said ready-made garments are Bangladesh's principal exports, accounting for 80 percent of its total exports. The country has about 4,500 such garment factories serving a number of international stores including the United States.