Human remains discovered in the Amazon rainforest were identified Friday as the missing British journalist Dom Phillips and Brazilian expert Bruno Pereira.
The pair were named after a laboratory examination of their teeth.
Regional police say they are working to "better understand the cause of death, the dynamics of the crime and the concealment of the corpses.”
Two suspects have been arrested. However, investigators said Friday they issued an "arrest warrant" for a third man wanted in connection to the crime.
His whereabouts are currently unknown, they said.
The bodies of Phillips and Pereira were found on Wednesday after one suspect led police to the site where they were buried. He had confessed to having buried them, although did not specify anything else.
Investigators have suggested that, based on the available evidence, "the killers acted alone, without a sponsor, without a criminal organisation behind the murders."
The Union of Indigenous Peoples of the Javari Valley (Univaja), whose members actively participated in the search, challenged this.
"There are not just two killers, but an organised group that planned the crime down to the smallest detail," Univaja said in a statement.
Phillips, 57, a renowned author and journalist, and Pereira, 41, an expert on indigenous communities, were in the Amazon to research a book on environmental conservation. Phillips is married to a Brazilian woman and had lived in the country for 15 years.
The two men were last seen 5 June, travelling through the northwestern Javari Valley, an area notorious for drug smuggling, illegal fishing and gold mining.
Univaja claims to have sent the authorities a report alleging that one of the suspects was involved in illegal fishing activities.
The Union alluded to "a powerful criminal organization which [has] tried at all costs to cover its tracks during the investigation," while calling for a "deepening" and continuation" of the police search.
"We demand the continuation and deepening of the investigations," they added.
Pereira, who had worked in the Brazilian government's department for indigenous peoples, previously said he had received multiple death threats.
The Javari Valley is the second-largest indigenous reserve in Brazil, lying in the heart of the Amazon rainforest.
26 indigenous communities live in the region, which is difficult to access and hard for the state to control. Police and military forces left the area shortly after the bodies were found.
The double murder of Phillips and Pereira has sparked outrage and condemnation around the world.
There has been strong criticism of far-right President Jair Bolsonaro, who supports mining and farming in indigenous reserves in the Amazon, for calling the pair's expedition an "unsavoury adventure."
On Friday, the US urged authorities in Brazil to find out who was responsible for killing the two men, "murdered for their support for the preservation of the rainforest and the indigenous populations."