Eight people are now suspects in the murders of British journalist Dom Phillips and indigenous expert Bruno Pereira, police say.
Three suspects have already been arrested.
But five more people who allegedly helped hide their bodies have now been identified, police told reporters.
Mr Phillips and Mr Pereira went missing while on a reporting trip in the remote Javari Valley in Brazil's far west on 5 June.
Their bodies were identified on Friday, after one of the suspects in custody - Amarildo da Costa de Oliveira - reportedly confessed to burying their remains and led police to a spot deep in the rainforest where their remains were found.
His brother, Oseney da Costa de Oliveira, was also arrested, but denies any involvement.
A third arrest followed on Saturday of a suspect named Jeferson da Silva Lima - also known as Pelado da Dinha - who turned himself in after going on the run, police said.
Brazilian news outlet O Globo reports that the five new suspects allegedly also helped to hide the bodies in a hard-to-reach area which police would have been unlikely to find if they had not been guided to it.
No names or further details on the new suspects have been given.
Police also said on Saturday that Mr Phillips and Mr Pereira had been shot by hunting ammunition. Mr Phillips was shot once, while Mr Pereira was shot three times, police added.
Mr Phillips - a regular contributor to the Guardian - was researching a book on the Amazon region. And Mr Pereira - who had extensive knowledge of indigenous communities - had been acting as Mr Phillips' guide and introducing him to contacts.
The Javari Valley region in which the two were travelling is home to thousands of indigenous people from more than 20 groups who live in isolation from the outside world.
The area is also known for illegal fishing, mining, logging and drug-trafficking activities.
Violent conflicts between these various criminal groups, government agents and indigenous people are known to happen, and were reportedly being documented by Mr Phillips and Mr Pereira.
Mr Pereira had also received death threats prior to taking the trip, indigenous rights groups said.