Two police officers engaged in the case told Reuters that Brazilian investigators are doubtful that remains found in a river belong to a British journalist who went missing in the Amazon rainforest on Sunday.

Federal police confirmed the discovery of "organic material" that was "apparently human," on Friday, heightening hopes for a breakthrough in the search for journalist Dom Phillips and his vacation partner, indigenous expert Bruno Pereira.

However, a federal police officer and a state investigator, who both requested anonymity to discuss the investigation, stated that the location and condition of the material cast doubt on whether it was connected to the missing men.

A representative for the federal police did not reply quickly to calls for comment.

According to accounts, the bones were discovered in the port of Atalaia do Norte, a town more than 65 kilometers (40 miles) downstream from where Phillips and Pereira were last seen on a slow-moving river. They stated that the nature of the debris suggested it may have been trimmings from a nearby butcher rather than remains washed downstream.

According to one of the sources, it was likely that the substance did not originate from a human. Still, it was submitted for forensic investigation out of caution. The other individual stated that this analysis would be necessary to determine the origin.

Sunday, according to witnesses, was the last time they saw Phillips, a freelance journalist who has written for the Guardian and the Washington Post. His companion Pereira, a local tribes specialist, had been a senior official at the government's indigenous agency, Funai.

The two guys were on a reporting mission in the isolated rainforest region near the Peruvian and Colombian border, home to the most significant number of uncontacted indigenous people in the world. The anarchic and rugged territory has attracted cocaine-trafficking gangs, illicit loggers, miners, and hunters.

The couple's absence has reverberated worldwide, with Pele and Caetano Veloso joining lawmakers, environmentalists, and human rights advocates in pressing President Jair Bolsonaro to intensify the search for them.

State police officers in the probe told Reuters that they are focusing on poachers and illegal fishers in the area, who frequently clashed with Pereira as he organized indigenous patrols of the local reservation.

Police have arrested one fisherman, Amarildo da Costa, also known as "Pelado," on a weapons charge and are holding him in custody as they investigate his possible involvement in the men's disappearance.

Costa's attorneys and family have stated that he fished legally on the river and denied involvement in the guys' abduction.

In addition to the indigenous search teams that had been searching for the two men since Sunday, approximately 150 soldiers were dispatched via riverboats to hunt for the missing men and interrogate locals.