Posting on social media on 10 September, Emma Kelty joked about a warning she had been given about the stretch of the Amazon river she was about to enter. “So in or near Coari (60 miles) I will have my boat stolen and I will be killed too,” she wrote. “Nice.”

Two days later, Kelty, who was canoeing the length of the Amazon, said she was “in the clear”. But hours later she posted again, describing an encounter with armed men. “Turned corner and found 50 guys in motor boats with arrows!!! My face must have been a picture!! (Town was uber quiet ... too quiet!!) all go ...

“OK 30 guys ... but either way ... that’s a lot of folks in one area in boats with arrow[s] and rifles.”

Three people held in Brazil on suspicion of British kayaker's murder Read more

The following day, as she neared Coari, on the banks of the Solimões river, an Amazon tributary, Kelty triggered a distress signal. She has been missing ever since. On Tuesday, police said they had arrested three males on suspicion of her murder.

Kelty, 43, from Finchley in north-west London, resigned as head of Knollmead primary school in Surbiton in 2014 to go travelling. No stranger to solo adventures, she had been only the sixth woman to ski solo to the south pole and hiked 2,600 miles alone across the US.

She had begun kayaking in February after deciding that her next challenge would be to paddle the Amazon from its source in the Peruvian Andes to the Atlantic Ocean.

There had already been unsettling moments in her trip, particularly since crossing the border into Brazil’s Amazonas state. On 22 August she told followers how she had paddled hard upstream to reach a beach to rest, “only to find a man waving a machete and ravens eating whatever he had killed. As I paddled hard away ... I could hear his shouts.”



In the following days she complained of broken sleep, interrupted by strangers. “Getting more tired every day,” she wrote on 23 August. “Let’s hope I don’t get [four] more guys ‘returning to visit me after dark’ tonight.”

Three days later, after a “great welcome” and day and night in São Paulo de Olivença, she reported that two men pitched up in a boat close to where she had stopped and just stayed there for two hours, stopping her from changing. “And yes, I did try to engage ... but they were the silent type.”

On 28 August she said she was “officially beyond triedness [sic]”. “Every night there has been a torch bearer and walker who comes to my tent,” she wrote. When strangers left her alone, Kelty fought “tent-bending” storms and 85% humidity. Yet there were also moments of tranquility.

“The last couple of days paddling was just what I imagined it to be,” she recounted on 5 September. “Now, I am sitting on my private beach in the sun. So quiet and just perfect.”

Emma Tamsin Kelty (@Emt101s) Enjoying a moments peace ... all is calm and just enjoying just being. #peru #so2017 #sourcetosea #riverlife #amaz… https://t.co/QFu0QAZkoq pic.twitter.com/Ak6CMLAFmO

Kelty is believed to have pitched her tent on Boieiro island, facing the town of Lauro Sodré, before she set off her locator flare last Wednesday. A 17-year-old suspect arrested on Monday in Codajás said that was where she was approached by two people. Five others arrived and the group stole her belongings. She was shot twice with a sawn-off shotgun and dumped in the river.

According to the teenager, whom police did not name for legal reasons, the group tried to sell her two mobile phones, her tablet computer and her GoPro camera in local communities. Another 17-year-old from Lauro Sodré was also arrested, as well as a third man, named as Erinei Ferreira da Silva, whose age was not given. Police are looking for four further suspects.

After Kelty’s distress call, authorities had launched a search operation involving 60 people, including divers scouring the riverbed. Residents of Lauro Sodré reported having seen Kelty alive, sailing past in her canoe. Fire officers and the Brazilian navy are continuing to look for her body and have searched the area where it was allegedly thrown.

Rocky Contos, a guide Kelty employed in Peru for the first six weeks of her trip, said he tried to warn her of the dangers she faced, but that she was determined to continue alone. “I told her there are people there who have no regard for life,” he was quoted as saying by the Times. “There are many cases of people being robbed and shot.”

River pirates are known to operate in the area where Kelty went missing. Local media reported two men were arrested in July after carrying out pirate attacks around Lauro Sodré and nearby communities.

“This region is a problematic region for pirates,” Barradas Júnior said. “It is a region that has pirates, they do robberies, and it is a disputed region because there are a lot of drugs coming from Colombia.” He said pirates had been known to attack Colombian and Peruvian drug traffickers, steal their supplies and throw their bodies in the river.

A struggle between rival Brazilian drug gangs to control the lucrative drug trade flowing down the Solimões river was blamed for a massacre in which 56 people were murdered in a prison in Manaus, capital of the state of Amazonas, on New Year’s Day. Dozens more were killed in reprisal attacks.

The remote stretch of the Solimões where Kelty is thought to have gone missing is the same section where the state’s previous civil police chief, Thyago Garcez, disappeared in December last year, after he and other police officers got into a firefight with drugs traffickers. His body has never been found.

The Foreign Office confirmed it was supporting the family of a woman who had died in Brazil and said it was in contact with the Brazilian authorities.

In a statement released by the Foreign Office, Kelty’s siblings, Piers, Giles and Natasha, said their “active and determined sister” had recently embarked on the Pacific Crest Trail in the US, and had also explored the south pole and finally the 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,” the statement said. “We are extremely proud of our sister who was dearly loved by us all and her strength will be sorely missed.”