Police said in a statement that seven arrest warrants had been issued for illegal fishing in the Vale do Javari region, the remote area near the border with Colombia and Peru where Phillips and Pereira disappeared on June 5.
The region has been invaded by illegal fishermen, loggers and gold diggers. Police say it is a key route for drug trafficking.
Phillips, a freelance reporter who has written for the Guardian and the Washington Post, was doing research for a book on the trip with Pereira, a former leader of the isolated tribes and recently contacted by the federal indigenous affairs agency Funai.
Two of the seven suspects were already under arrest: Ruben Dario da Silva Villar, known as “Colombia”, and fisherman Amarildo Costa de Oliveira, known as “Pelado”, who was arrested in June as the main suspect in the murder.
According to the police, Colombia is the leader and financier of an armed criminal gang involved in illegal fishing which was smuggled to neighboring countries.
Three of the newly arrested men, whose names have not been released, are relatives of Amarildo and were involved in hiding the bodies of Phillips and Pereira, police said.
Pereira, the former senior official at the federal indigenous affairs agency Funai, had previously clashed with Amarildo over illegal fishing in indigenous territory.
Federal prosecutors said Phillips was killed so he couldn’t identify the killers.