Three years after the British journalist Dom Phillips and the Brazilian activist Bruno Pereira were murdered in the Amazon, two major new projects will celebrate their lives and work – and the Indigenous communities and rainforests both men sought to protect.

Friends of Phillips have completed the book he was writing at the time of his death – How to Save the Amazon – which will be published in the UK, the US and Brazil on 27 May.

The book aims to highlight solutions for preserving the world’s largest tropical rainforest, focusing primarily on the experiences of its Indigenous peoples and other inhabitants. Phillips had completed less than half of it at the time of his death.

“Finishing it was important to show that Dom and Bruno’s voices were not silenced,” said Phillips’ widow, Alessandra Sampaio, who oversaw the project.

Meanwhile, a new Guardian podcast series, Missing in the Amazon, will be released on 5 June to mark the third anniversary of their murders in the remote Javari valley region.

The podcast is the fruit of a three-year investigation by Tom Phillips, the Guardian’s Latin American correspondent, who joined the 10-day search for Dom Phillips and Pereira after they vanished in June 2022.

“When discussing the case, everybody talked about the British journalist and the Brazilian Indigenous expert, but I don’t know if we ever really found out so much about who these men were,” said Phillips.

“I don’t think we ever heard so much from the people who loved them, cared about them and respected them – about who they were, where they came from, why they were doing what they were doing. And that’s something that we’ve tried to make a big part of the podcast,” he added.

“This podcast is about Dom and Bruno – told by the people who knew them best, many of whom are speaking for the first time,” said Nicole Jackson, the Guardian’s global head of audio.

“It’s also the story of what Dom and Bruno cared so much about: the Amazon and the Indigenous people who are trying to protect it. It’s about their future and the future of the world’s biggest rainforest.”

Pereira and Phillips were ambushed and killed near the Amazon town of Atalaia do Norte while returning from a reporting trip to the edge of the Javari valley, one of Brazil’s largest Indigenous territories. Soon after the men’s remains were found, Sampaio and some of Phillips’s closest friends decided to complete his unfinished book.

“Everybody deals with grief differently and, in this case, it was grief mixed with horror and anger,” said Jonathan Watts, the Guardian’s global environment editor, who helped plan the project, alongside Sampaio, Phillips’ literary agent, Rebecca Carter, and the journalists Andrew Fishman, David Davies and Tom Hennigan.

“Everyone knew that this book had to be finished,” said Fishman, a co-founder of the Intercept Brasil. “It would be completely unthinkable to let what happened to them be the end of Dom’s project.”

The first step in the process was understanding how much Phillips had already written.

Sampaio handed Fishman a black suitcase that had belonged to her husband, filled with reporter’s notebooks, laptops, old mobile phones and external hard drives.

“Dom was extremely organised, but not the greatest at encryption. So it was relatively easy to get all his work together,” he said.

Phillips’s notes, however, proved more challenging, due to his idiosyncratic handwriting; in the end they had to be “translated” by one of his sisters, Sian, and an old friend, John Mitchell.

Once they were able to review the material, the editorial team concluded that Phillips had completed the introduction and three and a half chapters – and left notes and outlines for another six.

The team decided the work should be completed by reporters who had known Dom and were also experts in covering the Amazon, selecting Tom Phillips, the Brazilian reporter Eliane Brum, former Reuters reporter Stuart Grudgings and the New Yorker’s Jon Lee Anderson.

The Indigenous leader Beto Marubo and activist Helena Palmquist wrote the afterword.

“It was an extraordinarily healing and uplifting process to get to know these people – these friends of Dom’s who I had had no connection with before,” said Carter, to whom Phillips first pitched the book in 2020. “We were suddenly very much united by his loss – and also the determination to make this happen.”

All of the contributors waived their fees, but to cover the costs of logistically complex reporting trips to the Amazon, the book relied on a fellowship from the Alicia Patterson Foundation (awarded to Phillips in 2021), grants from Whiting Creative and the Fund for Investigative Journalism, a donation from Teresa Bracher, and support from hundreds of crowdfunding backers.

Other journalists volunteered to edit the manuscript, and photographers contributed their images to the book. Dozens more supported the project in other ways – from factchecking to helping with outreach and social media.

Although it is Phillips’s book, Pereira is an essential character. The two men first met in 2018 during a reporting trip to the Javari for the Guardian, and Dom deeply admired Bruno’s work.

Investigations concluded that the killers had targeted Pereira in retaliation for his efforts to combat illegal fishing – often backed by organised crime – in the Javari valley.

The murders took place during the environmentally catastrophic 2019-2023 administration of the far-right president Jair Bolsonaro, who was widely criticized for his sluggish response to the disappearances of Phillips and Pereira and called their trip “an ill-advised adventure”.

Since defeating Bolsonaro in the 2022 election, the leftist president Luiz Inácio Lula da Silva has made the Indigenous cause and the Amazon priorities, launching major operations to evict illegal miners from areas such as the Yanomami and Kayapó territories and achieving a major reduction in deforestation.

However, Marubo – who was close friends with Pereira and works for the Javari valley Indigenous association – said that despite noticeable improvements since Bolsonaro’s departure, Lula’s efforts were still falling short: “You can’t fight illegality and the spread of organised crime with two or three isolated operations … We need government action that is continuous and coordinated,” he said.

“Unfortunately, if Dom and Bruno were working here today, they would be killed again,” he said.

Three local men were later charged with their murders, while a fourth has been charged with ordering the crime. All are in custody awaiting trial.

“I strongly believe in justice,” said Sampaio, Phillips’s widow. “We hope for things to move more quickly, but my lawyers have told me that the case is progressing as it should,” she said.

Sampaio, Marubo and other book contributors have travelled to the UK to take part in launch events at the Hay festival (31 May), in Lancaster (3 June) and in London (5 June).

“It makes me very happy that the book has been completed,” said Sampaio. “We carry on with the sadness, but we carry on because we must.”

• How to Save the Amazon: A Journalist’s Deadly Quest for Answers is published in the UK, US and Brazil on 27 May. The first two episodes of Missing in the Amazon will be released on 5 June.