Five more arrested in Brazil over murders of Dom Phillips and Bruno Pereira | Dom Phillips and Bruno Pereira

Brazilian police arrested another five people in connection with the murders of British journalist Dom Phillips and Brazilian Indigenous activist Bruno Pereira on Saturday, and said one of the suspects already in custody was likely the leader of an illegal mafia based in the Amazon region.

Although they gave a few details, police said three of those detained in operations near Brazil’s borders with Peru and Colombia were wanted for helping bury the bodies of Phillips and Pereira.

All three are related to Amarildo da Costa Oliveira, one of three men charged last month with the double murder in a case that shocked the world and highlighted growing in security in the densely forested region.

Phillips, 57, and Pereira, 41, went missing in the Javari valley in western Brazil on 5 June, at the end of a trip Phillips had arranged to report a book about sustainable development. Phillips had written for the Observer and the Guardian as well as other publications.

Pereira, a former official with Brazil’s state Indigenous agency, knew the area well and was helping the Briton with his research.

The men were ambushed early one morning as they headed down the Itaquaí river on their boat. Police believe their assailants shot them dead and then carried their bodies into the jungle, where they buried them in the hastily dug grave.

However, two of the suspects confessed to the crime and led police to where they had buried their bodies.

Police believe the killers were worried that Pereira had photographs and evidence they were fishing in prohibited areas for endangered species, including turtles and pirarucu, one of the world’s largest freshwater fish.

One single pirarucu can fetch up to $1,000 at markets in Brazil and Colombia and police believe criminal mafias partner with impoverished local fishers to hunt the animals, often in Indigenous reserves where access to outsiders is prohibited.

They arrested one man last month for using false ID papers and on Saturday said they had identified him as Ruben Dario da Silva Villar, AKA “Colômbia”.

Police “found strong indications that Colômbia is the leader and financier of an armed criminal association dedicated to the practice of illegal fishing in the Javari valley [and] responsible for the sale and export of a large amount of fish”, the federal police said in a statement.

Local news reports said da Silva Villar provided the local fisher with boats, motors and bait.

Indigenous housing in the region welcomed the news “with great joy” and said it marked “the beginning of justice”.

A lawyer for the Univaja Indigenous Organization said the arrests, and particularly that of Colômbia, confirmed their original thesis – that the killings were not carried out by individuals working alone, but with the collaboration or orders of a local mafia.

“A criminal organization has been working in the Javari valley for a long time and today’s investigation, operation and arrests merely reinforce that,” said Eliesio Marubo, Univaja’s lawyer. “So we feel represented. This is the start of justice for our friends who were brutally murdered.”

“This reinforces the need for the state to participate in an area that was abandoned by the state,” he added.

The investigation continues.