The Brazilian police say they have arrested a second suspect in connection with the "alleged murder" of British journalist Dom Phillips and Brazilian indigenous rights activist Bruno Pereira.

Oseney da Costa de Oliveira, 41, was detained on Tuesday and is held in Atalaia do Norte. When they vanished, the remote river hamlet Phillips and Pereira were attempting to reach on June 5.

Oliveira, whose nickname is "Dos Santos," was arrested "on suspicion of involvement in the case," along with his brother Amarildo da Costa de Oliveira. The latter has been detained since last week.

Alex Perez, the chief of civil police, informed reporters outside the police station where both men are currently being held that he was arrested at his residence in Atalaia do Norte and did not resist arrest.

"Witnesses placed them both at the alleged crime scene," said Perez, surrounded by rifle-wielding police and federal police agents.

When asked by the Guardian for what actual crime the suspect had been apprehended, Perez said, "suspect of aggravated murder" (suspect of aggravated murder).

Investigators believe Pelado, also known as Amarildo da Costa de Oliveira, was responsible for ambushing Phillips and Pereira on the Itaqua River as they returned from a four-day reporting expedition.

During the execution of two search warrants, federal officers seized several gunshot casings and an oar, according to their report. On Tuesday afternoon, forensic officers were spotted arriving at the port in Atlaia do Norte with an oar as the hunt for Phillips and Pereira proceeded in an area of flooded forest where indigenous volunteers discovered a number of the men's belongings on Saturday.

According to reports, Pelado has denied involvement in the disappearances. The Brazilian daily O Globo said on Tuesday that he stated during interrogation that he had not left his home in the riverbank community of So Gabriel on the day the men disappeared.

The suspect confirmed he had seen Pereira's boat on the day of the disappearance but claimed he had not been out on the water until the next day when Pelado claimed he had gone pig hunting in his boat.

According to police sources, Pelado and four others were observed pursuing Phillips and Pereira down the river in his boat. Investigators have been attempting to identify these individuals.