“One day,” Behrouz Boochani said, observing the bleakness of the abandoned Manus detention centre, its dark form illuminated by wood stripped from the buildings being burned for light, “we will meet in some other place, far away from here.”

That was two years ago, in the middle of a warm November night, when Boochani helped smuggle this reporter into the decommissioned Manus Island detention centre where 400 men were holding out against being forcibly removed: rationing their dwindling supply of food and medicine, guarding against the violent police crackdown they knew was coming, repairing the freshwater wells that had been deliberately spoiled by the retreating guards.

“One day,” he said.

Play Video 4:28 Behrouz Boochani: how I got out of my Manus Island hell – video

Today is that day. Behrouz Boochani is in that other place. He stands in the sunshine in Christchurch’s botanical gardens, a man at liberty, a broad smile creasing his worn features. In this city, people stop Boochani in the street to talk, they reach out to touch his arm and say “welcome”. He is moved to tears.

“Here,” he says, “I feel free.”

Boochani has arrived in New Zealand a free man. The Kurdish Iranian journalist, author and filmmaker who has done more than any other person to document Australia’s offshore detention regime – from the inside – still faces an uncertain future.

Decay, despair, defiance: inside the Manus Island refugee camp | Ben Doherty Read more

Long years of listless detention have given Boochani, naturally introspective, an acute sense of his emotions.

Behind the high steel fences of the Manus Island detention centre, his moods could swing dramatically, from a wild, garrulous mania fed by simultaneous WhatsApp conversations all over the world, to a black and shiftless depression whose silence could take weeks to lift.

He was laid low by illness, dispirited by incarceration, reduced to a shell by two bouts of torture in the infamous Chauka solitary detention centre. (His crime: to report the torture of others to the outside world.) The uncertainty of indefinite detention took its toll. Gradually, and all at once.

Each time the Guardian met Boochani on Manus, he presented a little more diminished: physically smaller, his head bowed, his shoulders hunched, as though he felt he took up too much room on that foreign island, that place he could never belong.

Facebook Twitter Pinterest Behrouz Boochani in his early years of detention on Manus Island.

Always lean, he lost a dangerous amount of weight in detention, his piercing eyes set further into his lined face, his voice a little more retreated into his chest.

In detention, Boochani said several years ago, he could sense when his mental state was beginning to slip from his control, but he felt powerless to stop it. He found the one thing that could arrest the slide was the thing that always had: writing.

So he wrote.

He wrote prose, he wrote poetry, he wrote song lyrics. He wrote a book, famously tapping it into a mobile phone on WhatsApp and sending it overseas, where it was collated and translated. No Friend But the Mountains – the title drawn from an old Kurdish proverb – would win the Victorian literature prize.

Boochani filmed a documentary, Chauka, Tell us the Time, shot by shot, on a smartphone kept hidden from guards. It would screen across Australia, in Berlin and in London.

He told the story of the Manus Island detention centre to the few who would listen at first, to the many who came to understand the reality of that place, to the whole world when given his chance.

Boochani became the voice of Manus, the irrepressible and authoritative account of Australia’s offshore regime, told from inside the wire.

‘I thought Australia was free’

Boochani is now 36. An ethnic Kurd from Ilam in the west of Iran, bordering Iraq, he was forced to flee his homeland after his journalism for the Kurdish magazine Werya (also spelled Varia) attracted the attention of Iran’s ruling regime.

He realised early in his career the power, and the danger, of journalism.

Werya was iconoclastic in its defiance of the Tehran regime, publishing articles celebrating Kurdish language and culture, and in support of Kurdish political independence. Boochani was arrested by the Iran’s Sepah – known formally as the Army of the Guardians of the Islamic Revolution – in 2011 and warned to stop writing. He did not.

Two years later, when the Sepah raided the offices of Werya and arrested 11 of his colleagues, Boochani, who was away from the office at the time, published the story of his colleagues’ arrest and detention on a website called Iranian Reporters. His story probably won them their freedom, but it put him in danger.

“They were excited and scared,” Boochani told the Guardian in an earlier interview. “They said ‘Behrouz, if you did not publish that news they would have killed us’. They said ‘Thank you [but] please take care. They will arrest you. They asked us many questions about your ideas.’ I didn’t want them to arrest me.”

Boochani chose to flee. He chose Australia.

“I did not sleep for two months, but then I left Iran. It was so dangerous for me. I thought if I can publish my ideas in a free country then I can help my people. I thought that Australia was free.”

On 23 May 2013 Boochani left Iran, travelling through south-east Asia and then by boat to Christmas Island, arriving in July. He was transferred to Manus on 27 August 2013.

There, over the course of six years in PNG, Boochani became a tireless campaigner for the rights of those held by Australia.

Held on Manus Island and in Port Moresby, Boochani witnessed friends shot, stabbed and murdered by guards, saw others die through medical neglect, and watched others as they descended into mental anguish and suicide.

He was twice held for several days in the notorious Chauka solitary confinement block within the since-demolished Manus detention centre, where he was beaten and, in his description, “tortured” by those employed to protect him. He was jailed for eight days for reporting on a hunger-strike within the centre that was put down by force by PNG police.

Facebook Twitter Pinterest Boochani outside the detention centre where he was held for the first three years on Manus Island. Photograph: Jonas Gratzer/LightRocket via Getty Images

But throughout, he maintained a role as a working journalist on the island, the most prominent – and, initially the sole – voice from within the secretive regime.

“I am a journalist,” he told the Guardian in 2015. “I am still a journalist in this place. This is my work, my duty.”

That duty gave him a purpose on Manus, a role and a reason to get out of bed. As others’ mental health succumbed to the cruelty and capriciousness of the offshore regime, Boochani remained, by comparison, far more level-headed.

Boochani became a regular correspondent for the Guardian and other news outlets, leading detailed investigations based on eyewitness accounts, interviews inside detention and leaked documents.

'Six years and I didn't achieve anything': inside Manus, a tropical purgatory Read more

With strong English, a journalistic background and a keenly articulated sense of the language of human rights and democracy, Boochani was an obvious candidate to be the messenger of Manus.

But he could never escape being one of the men held inside.

“I cannot just walk away from that place,” Boochani now says.

“There are many pictures in mind, some of the memories are so so difficult for me, I think of one of them often, one of the men who died was Faysal Ishak Ahmed [who died after collapsing in December 2016 after being rebuffed more than a dozen times from the detention centre medical care, accused of malingering]. When Faysal died, one of the sick men, a Rohingya man, Salim, came to me, he said that ‘I have blood problem too, I am worried that I will die in the way that Faysal died.’

“And it was so difficult, because what can I do? I was in that place too. I was powerless to help him. That man died later. He committed suicide. He did not want to die like Faysal died. Everyone in Manus carries these painful memories, we can never leave them on that island.”

‘At that time, it was like a warzone’

Boochani’s attitude towards Australia is complicated. He has many friends there, and knows the contours of its politics and people intimately. His name is known and recognised across the country. But, other than a few days behind wire on Christmas Island, he has never set foot in the place. He likely never will.

He says he has nothing to say to the Australian governments – Labor and Liberal – that detained him on Manus. But he says he feels, in many ways, Australian.

“I have nothing to say to the Australian government. But what I would like to say to the public is: Manus and Nauru are a part of Australia forever, and you cannot deny this.

Behrouz Boochani (@BehrouzBoochani) Such a rediclilius and unacceptable statement by Labor Party. You exiled me to Manus and you have supported this exile policy for years. I don't need you to welcome resttlement for me in a third country. https://t.co/XHIBCcrUQY

“I don’t know that in the future I will have the opportunity or not to visit Australia. But I am Australian, as much as somebody like Peter Dutton. Because he played with the Australian international reputation, he damaged this country, he damaged this democracy. I, as a stateless person, will never go to Australia, but I spoke to Australians, I participated in events at universities, I wrote to the Australian people, to share the story of their Manus. I tried to make Australia a better place. That’s why I am an Australian, as much as someone like Dutton.”

Boochani had initially vowed he would remain within the strictures of Australia’s offshore detention regime until all were liberated from it. He felt a duty. When the men (and, apart from its first few months, the Manus detention centre was only for adult men) were all held together, an unshakeable solidarity emerged among the detainees that erased ethnic, religious and language divides.

Facebook Twitter Pinterest Behrouz Boochani talks to the Guardian’s Ben Doherty in Christchurch on Friday. Photograph: David Fanner/The Guardian

The strength of that solidarity was recognised by the authorities running the camp, who split the population with tall metal fences, and capriciously moved people from one to the other in an attempt to disintegrate friendship groups.

“At that time, it was like a warzone: people relied on each other a lot,” Boochani says. “We had this brotherhood culture in Manus, because we needed that to survive. But now everyone is separated, it is much harder.”

Over recent months, with the decommissioning of the centre, and the spread of refugees across PNG, to America, and to Australia, that solidarity is fracturing. There is little more Boochani feels he can do. And he is tired.

“There are painful stories, everyone from Manus carries these kinds of stories … but I am happy in my heart. I always tried to work honestly, to be independent and to bring the truth to the light. I am very, very tired.

“I did my best.”

‘I cannot walk away’

There is much adjustment ahead for Boochani as he comes to terms with life at liberty, wherever that may be. He has a visa for a month: a more certain freedom than he has known for years. He remains hopeful he can resettle in the US – which has technically accepted him as part of Australia’s “refugee swap” deal with America.

But there is a very real possibility Boochani’s US offer – already slow-moving and, to his mind, always precarious – might be withdrawn because he has left PNG.

If the US offer is revoked, Boochani says “I will look at possibilities”, which may include yet another application for asylum in yet another country, possibly in Europe.

On Friday the deputy chief executive of Immigration New Zealand, Greg Patchell, ruled out Boochani being granted an extension of his one-month visitor visa in NZ, stating “he must depart before his visa expires”.

Christchurch’s November sun is a little cool for a man grown used to the tropics. And he misses, in a nostalgic way, the fierce monsoons of Manus.

“I have always loved rain,” he says. “My father was a farmer, he depended on the rain, and he used to look, always, to the sky. When it rained he was happy – rain makes me happy.” The sky in Christchurch is a cloudless and brilliant blue.

Most of all, Boochani misses those he was forced to leave behind.

Boochani says about three-quarters of the refugees and asylum seekers sent to PNG by Australia from 2012 have left – to Australia, the US or other countries. Seven have died through murder, medical neglect or suicide. But Boochani says he is distraught that some remain trapped there, in particular 46 who are being held, essentially incommunicado, in Bomana prison in Port Moresby.

Boochani says they will not be forgotten, nor will his time on Manus, for all of the heartache and hurt that it brings.

“It is like a duty, a responsibility, as a citizen in my future, to care about human rights. I will continue to work on this issue, because it is my life, I cannot walk away from my own life, my own experience. And Manus was my experience.”