British kayaker Emma Kelty was shot by a gang of seven men who then threw her body into the Amazon while she was still alive, say Brazilian police.
The 43-year-old, from London, had been attempting to travel the entire length of the Amazon on her own.
She was killed last week in an area known for drug traffickers and pirates. Police said one of the men thought responsible has also since been killed.
Police have arrested three men over her murder. Her body has not been found.
The former headteacher was camping by in the upper stretches of the river in northern Brazil on 13 September when she was spotted by a gang of “pirates”, who were in a canoe, police said.
They fired two shots at her tent from a 20 calibre rifle before stealing her belongings, including a drone, two mobile phones and a tablet.
Locals reported seeing Ms Kelty still alive as she was taken, by canoe, into the middle of the river before being thrown into the water.
Lead investigator Jose Afonso Barradas said the men tried to sell her possessions and “were heard boasting about having a lot of money and gold”.
One of the men, Evanilson Gomes da Costa, is believed to have been responsible for firing the rifle at Ms Kelty – according to Brazilian police he died on Wednesday after also being shot.
Police said it was likely he was killed by a rival gang who were trying to get hold of Ms Kelty’s stolen cash.
Jardel Pinheiro Gomes, 19, Erinei Ferreira da Silva, 28, and a 17-year-old boy have been arrested and police are still looking for three other men.
The Brazilian Navy and divers from the Amazon fire brigade are searching for Ms Kelty’s body.
Her kayak was found by police, who are still trying to recover her stolen belongings.
Ms Kelty was 42 days into a 4,000-mile trip along the Amazon river, which she had been documenting on social media, when she was attacked.
Just a few days before her death, she wrote on Twitter about the dangers of the area she was enteringon Twitter: “So in or near Coari (100km away) I will have my boat stolen and I will be killed too. Nice.”
Her family said they were extremely proud of her and “her strength would be sorely missed”.
Ms Kelty’s brothers Piers and Giles, and sister Natasha, said in a statement: “Emma was an active and determined sister who challenged herself, latterly through her adventures on the Pacific Coast Trail, as well as in the South Pole and Amazon River.
“In a world that is today a much smaller place, the explorer in our sister found herself seeking ways to prove that challenges were achievable.
“We wish to give our immense thanks to the Brazilian Navy, police and Foreign Office for their action and support.”