According to a Brazilian federal police statement, six rifles, multiple automatic weapon magazines, two boats, seven vehicles and an unspecified cash amount were seized in the operation to arrest the suspects.
The robbery happened early Monday in Paraguay, near the border with Brazil and Argentina, police said.
Dozens of gunmen detonated explosives and set vehicles on fire as they stormed the company in Paraguay, taking millions of dollars and sparking a violent police chase into Brazil.
More than 50 people carrying large caliber weapons, dynamite and caltrops took part in what authorities are calling the "robbery of the century."
The group made off with money from several vaults inside Prosegur, a private security firm in Ciudad del Este, police said.
In initial reports, police said the vaults were able to store up to $40 million but neither authorities nor the firm confirmed the sum that was taken.
Ciudad del Este is Paraguay's second-largest city and is along the border with Brazil and Argentina.
Authorities believe the robbers were members of Primer Comando de la Capital, one of the largest criminal organizations in Brazil.
A police officer was killed during Monday's shootout that started about midnight (local time) and lasted for about two hours. Another officer and three bystanders were injured and taken to local hospitals, police said
Grenades were set off and more than a dozen vehicles were set on fire as the robbery took place. Police said officers engaged in a gun battle with snipers and others armed with large caliber weapons, dynamite and caltrops.
In a building next to the security firm, Alejandro Anisimoff and his family hid when the robbers broke into their home.
"We heard non-stop turmoil for an hour. Within that hour, five grenades blew off here. We hid upstairs in one of the bedrooms," Anisimoff, whose home is in the building next to the firm, told CNN en Español.
Leaving mass destruction behind them as they fled police, the robbers were able to cross the border into Brazil. A small group was intercepted by Brazilian police in a region called Itaipulandia, about 50 miles from Ciudad del Este, officials said.
Three suspects were killed and four arrested during the confrontation, said a spokesperson with Paraguay's Interior Ministry in a news release
The building had been under the police radar before, Richard Vera, chief of the Ciudad del Este police homicide department, told Argentina's El Pais newspaper.
In 2015, they found an L-shaped tunnel connecting the building to a nearby house.