Brazilian police have named the alleged mastermind behind the murders of the British journalist Dom Phillips and the Brazilian Indigenous expert Bruno Pereira in the Amazon last year.

Rubens Villar Coelho, whose nickname is Colômbia, was first arrested on separate charges last July – one month after the two men were murdered in the Javari valley region of the Amazon. He was released in October but was rearrested last month for breaking his bail terms.

On Monday afternoon, the federal police chief for Amazonas state, where the Javari valley is located, told reporters that investigators had concluded Villar Coelho – who has been accused of running an illegal fishing racket in the remote border region – had ordered the murders.

“I have no doubt that Colômbia was the mastermind,” Alexandre Fontes said at a press conference in the state capital, Manaus, according to the Brazilian news website G1.

Three other men are currently in custody for the murders and stand accused of shooting Phillips and Pereira as they travelled down the Itaquaí River on the morning of 5 June 2022. They are Amarildo da Costa Oliveira, Jefferson da Silva Lima and Oseney da Costa de Oliveira.

Fontes said investigators had gathered evidence that Villar Coelho provided the first two of those men with the ammunition that was used to commit the murder.

Fontes claimed the ​16-gauge shotgun used in the crime had been provided by Amarildo da Costa Oliveira’s brother, Edvaldo da Costa Oliveira, “in the knowledge that it would be used to murder Bruno and Dom”.

Villar Coelho had also paid for Amarildo da Costa Oliveira’s initial defense lawyer, Fontes added.

Villar Coelho denied involvement in the crime after being detained last July.

Phillips, 57, a longtime Guardian contributor and foreign correspondent, travelled to the Javari valley with Pereira as part of research for a book he was writing called How to Save the Amazon.

At the time of the murders, 41-year-old Pereira, a revered Indigenous specialist and explorer, had been helping Indigenous communities in the Javari valley set up monitoring teams to defend their rainforest homes from illegal mining, poaching and fishing gangs with links to organized crime.

The murders sparked international outrage and exposed the damage done to Brazil’s environment and Indigenous communities during the far-right government of Jair Bolsonaro, who lost last October’s election and is currently in the US.

On Sunday, Bolsonaro’s successor, Luiz Inácio Lula da Silva, accused the rightwing populist of committing genocide against the Yanomami people of the Amazon by dismantling Indigenous protections and encouraging the illegal gold miners who have invaded that and other Indigenous territories.

Speaking to the Guardian recently in Brasília, Beto Marubo, a Javari leader who was close to Pereira, said Indigenous activists had seen no sign of the security situation improving in the region despite the outcry over the murders.

Marubo voiced hope that the men’s killers would be brought to justice under Brazil’s new government.

“We hope – and we will continue to demand from the new government​ and authorities​ – that there is justice for Dom and Bruno​,” he said.

Relief that police had formally accused Villar Coelho, a notorious and feared figure in the region where Phillips and Pereira were killed, was tempered with ongoing suspicions that their murders were part of a bigger conspiracy in a region awash with environmental crime and drug trafficking, reportedly involving cartels from Colombia and Mexico.

The Javari valley, which is home to the world’s largest concentration of isolated Indigenous tribes, has become a major highway for cocaine and marijuana smuggling in recent years, with huge shipments of drugs being moved by river from Peru into Brazil and then on to Europe.

Eliesio Marubo, a representative of Univaja, the Indigenous NGO for which Pereira had worked, said the federal police conclusions had confirmed the murdered activist’s suspicions that Villar Coelho was involved in the fishing gangs that preyed on the supposedly protected Javari valley Indigenous territory. But Marubo said many questions remained.

“Who is bankrolling these people so they are able to continue their criminal activities? Why is it that so many politicians in the region helped these criminals? Why is this criminal organization still operating in the region?” he asked, pointing to a November attack on another of the Javari’s Indigenous leaders.

Marubo said Javari activists wanted a “far-reaching investigation” which “truly showed who killed Dom and Bruno”.