Police say cracks in the building had led them to order an evacuation Tuesday, but the factories ignored the order and were operating when it collapsed Wednesday. Video shot before the collapse shows cracks in the walls, with apparent attempts at repair. It also shows columns missing chunks of concrete and police talking to building operators.
Officials said soon after the collapse that numerous construction regulations had been violated.
Abdul Halim, an official with Savar's engineering department, said the owner of Rana Plaza was originally allowed to construct a five-story building but added another three stories illegally.
Mahbubul Haque Shakil, a spokesman for Prime Minister Sheikh Hasina, said she had ordered police to arrest the owner of the building as well as the owners of the garment factories in "the shortest possible time."
Local police chief Mohammed Asaduzzaman said police and the government's Capital Development Authority have filed separate cases of negligence against the building owner.
Habibur Rahman, police superintendent of Dhaka district, identified the owner of the building as Mohammed Sohel Rana, a local leader of ruling Awami League's youth front. Rahman said police were also looking for the owners of the garment factories.
Police on Friday detained two of Rana's relatives for questioning, police officer Mohammad Kawser said.
The disaster is the worst ever for Bangladesh's booming and powerful garment industry, surpassing a fire five months ago that killed 112 people and brought widespread pledges to improve the country's worker-safety standards.
Instead, very little has changed in Bangladesh, where wages, among the lowest in the world, have made it a magnet for numerous global brands.
Bangladesh's garment industry was the third-largest in the world in 2011, after China and Italy. It has grown rapidly in the past decade, a boom fueled by Bangladesh's exceptionally low labor costs. The country's minimum wage is now the equivalent of about $38 a month.
Among the garment makers in the building were Phantom Apparels, Phantom Tac, Ether Tex, New Wave Style and New Wave Bottoms. Altogether, they produced several million shirts, pants and other garments a year.
The New Wave companies, according to their website, make clothing for several major North American and European retailers.
Britain's Primark acknowledged it was using a factory in Rana Plaza, but many other retailers distanced themselves from the disaster, saying they were not involved with the factories at the time of the collapse or had not recently ordered garments from them.
Wal-Mart said none of its clothing had been authorized to be made in the facility, but it is investigating whether there was any unauthorized production.
U.S. State Department spokesman Patrick Ventrell said the collapse underscored the "urgent need" for Bangladesh's government, as well as the factory owners, buyers and labor groups, to improve working conditions in the country.
Human Rights Watch says Bangladesh's Ministry of Labor has only 18 inspectors to monitor thousands of garment factories in the sprawling Dhaka district, where much of the nation's garment industry is located.
John Sifton, the group's Asia advocacy director, also noted that none of the factories in the Rana Plaza were unionized, and that had they been, workers would have been in a better position to refuse to enter the building on Wednesday.