The family of a 70-year old Australian man convicted of terrorism by a Vietnamese court say his 12-year prison term is “a death sentence” and fear they may never see him again.

Human rights advocates, lawyers and Chau Van Kham’s family say the charges against him are baseless and politically motivated, his single-day multiple-defendant trial was grossly unfair, and his failing health means he may not survive.

On the walls of the Chau family home in suburban Sydney hang pictures of an absent man.

Chau’s wife has not seen her husband, not heard his voice, since he was arrested in January.

“Please ... bring him back, bring him back to me,” Quynh Trang Truong says haltingly, through tears.

“I just want him home. Before he gets too old, before he is too unwell, I am worried he will be too sick.”

Quynh has written to Scott Morrison, “filled with both faint hopes and great despair, to seek your valuable help … so my husband can be released and reunited with his family in Australia”.

Australian retiree convicted of terrorism and jailed for 12 years in Vietnam Read more

“He is a hard-working citizen, and he deserves the Australian government’s support in this painful circumstance.”

Qunyh said in the letter her husband was innocent of the charges of terrorism.

“I believe you have already known very clearly this is an absolutely false and groundless allegation against my elderly husband.”

Chau’s son Daniel tells Guardian Australia his father’s serious health conditions have deteriorated badly in prison and his isolation has heightened his family’s fears.

“Twelve years is pretty much a death sentence. Dad is suffering.

Facebook Twitter Pinterest ‘I just want him home,’ says Quynh Trang Truong, pictured with son Daniel Chau. Photograph: Jessica Hromas/The Guardian

“We’ve not been able to speak directly to him since he was arrested on 15 January. We saw pictures of him at the trial, he looks pale, I don’t think he’s physically OK. Even though the guards say he’s getting treatment, just his face at his trial, he doesn’t look healthy to me.”

Quynh and Australian lawyer Dan Phuong Nguyen, who is acting pro bono for the family, travelled to Canberra this week for meetings with parliamentarians and representatives from the Department of Foreign Affairs and Trade. Quynh says she was grateful for the official attention to her husband’s case, and hopeful Australian government entreaties might yield a breakthrough.

She says her family would accept an immediate deportation order and a commitment Chau would never return to Vietnam, in exchange for his liberty.

UN reprieve: asylum seeker faces separation from baby if she is deported from Australia Read more

In prison in Ho Chi Minh City, Chau has only been allowed to see one relative, his sister – who lives in Vietnam – on two occasions since being arrested. A niece who flew to Vietnam for the trial was refused entry to see him in prison and denied access to the courtroom where he was tried and sentenced at his first appearance in a single-day judge-only trial alongside five other defendants.

Chau, a naturalised Australian citizen, was born in Vietnam and served in the army of the Republic of Vietnam before 1975. After the war, he was sent to a re-education camp for three years, before he fled Vietnam by boat, arriving in Australia in 1983.

In Sydney, he worked as a baker for decades, rising before dawn to be at work at a modest suburban bakery.

Facebook Twitter Pinterest A family photo from several years ago shows Quynh Trang Truong (left), Chau Van Kham (centre back) and their children, Dennis Chau (middle) and Daniel Chau (right). Photograph: Supplied by the family.

In his retirement he took to growing long rows of dragon fruit in his backyard for neighbours and local markets, and he turned to democratic activism.

He became prominent in the Australian wing of Viet Tan, a political organisation dedicated to the democratisation of Vietnam, and a vocal campaigner for increased transparency and civil rights.

In the 1980s, Viet Tan advocated toppling Vietnam’s communist government through popular uprising, but in recent years it has explicitly rejected the use of violence, stating the organisation is “convinced that nonviolent means are most effective … to contribute to Vietnam’s modernisation and reform”.

Chau only joined Viet Tan in 2010, but became a key organiser of pro-reform rallies and an outspoken advocate for democratisation in Vietnam.

He sought to return to Vietnam in January 2019 to meet fellow pro-democracy advocates but was refused a visa by the Vietnamese government.

He chose to cross into Vietnam via a land border with Cambodia, carrying false documents against his wife’s urging.

“I told him ‘don’t go into Vietnam’, but he still went, he wanted to see the country.”

Facebook Twitter Pinterest Quynh Trang Truong urged her husband not to go back to Vietnam. Photograph: Jessica Hromas/The Guardian

Chau’s son Daniel says his visit to Vietnam was a “fact-finding mission”.

“The only rule he broke was he had the wrong documents. He had no ill intent to cause trouble or anything like that. He just wanted to see the situation on the ground.”

Chau met a fellow democracy activist who, it is believed, was under surveillance. Chau was later arrested, along with Vietnamese nationals Nguyen Van Vien and Tran Van Quyen, who were sentenced to 11 and 10 years respectively.

'Atrocity of the century': Uighur activist urges Australia to take tougher stance against China Read more

Chau was initially charged with participating in activities aimed at overthrowing the government, but in July, this was downgraded slightly to “terrorism to oppose the people’s government”.

At their extremes, both charges carry the potential of execution under Vietnam’s penal code, but long prison sentences (Chau’s is considered heavy, but not extreme) are the most common punishment.

Despite sweeping economic reforms and an increasing openness to social change, Vietnam’s ruling Communist party retains tight media censorship and does not tolerate political criticism both within and from outside Vietnam. Viet Tan is proscribed as a terrorist group by the Vietnamese government, but the United Nations describes it as “a peaceful organisation advocating for democratic reform”.

Vietnam’s Ministry of Public Security said in a statement Chau was convicted of holding a senior position in the New South Wales chapter of Viet Tan, for “financing terrorism” and for recruiting new members to the movement.

Facebook Twitter Pinterest Daniel Chau said his father travelled to Vietnam with no ill intent. Photograph: Jessica Hromas/The Guardian

“This is a very serious case of national security infringement led by Viet Tan’s key people,” prosecutors told the court.

“It’s all just a lie,” Chau’s son Daniel says of his conviction and sentence. “It’s just another excuse to squash opposition to their rule, regardless of whether it’s legitimate or not.”

In a letter to the foreign affairs minister, Marise Payne, urging the Australian government to more forcefully press Chau’s rights, Human Rights Watch Australia director Elaine Pearson said there were severe flaws in Chau’s trial and conviction.

Having been arrested in January, Chau was not allowed to see a lawyer until October. All of his meetings with consular officials have been recorded on camera and undertaken in the presence of prison and other government officials, Pearson wrote. No evidence was presented in court documents, or during his trial, of any plans to engage in any violent, seditious or terrorist act.

In addition to Chau, Nguyen and Tran, three further people were sentenced for manufacturing false documents. All six were tried and convicted in a single trial before a lone judge.

Yang Hengjun: Chinese officials try to 'break' Australian writer with daily interrogations Read more

“The trial lasted only four-and-a-half hours, suggesting the verdict was pre-determined,” Pearson wrote. “With six defendants, the court would barely have enough time to carry out normal process including reading the names and charges, let alone listening to presentation of evidence and defence arguments in a fair and unbiased manner. All Vietnamese judges are required to be members of the Communist party of Vietnam.”

Chau’s Vietnamese lawyer Nguyen Van Mieng says Chau professed his love for Vietnam during his trial and told the court he never had “any intention to carry out terrorism activities in the country”.

“The prosecutors stuck to the idea that he’s a member of Viet Tan to charge him with terrorism. The jail terms for political prisoners are getting longer and longer,” he says.

Facebook Twitter Pinterest Chau Van Kham was sentenced to 12 years’ jail in Vietnam for ‘terrorism’. Photograph: Supplied by the family.

In a statement, Viet Tan condemned Chau’s hearing as a “sham trial”.

“Viet Tan will continue to support human rights defenders on the ground. Chau Van Kham entered Vietnam to gain first-hand insight into the human rights situation in the country,” the organisation’s chairman, Do Hoang Diem, said in the statement.

Chau has lodged an appeal against his conviction and sentence, but he has not been allowed to see a lawyer to prepare.

“Even if Dad fills the forms out, goes through the procedure correctly, I worry they will just palm it off,” Daniel Chau says. “There’s just no way he will get a fair trial.”

The Australian government’s ability to assist citizens arrested overseas is often limited, but the government has brought significant political pressure to bear on other countries, such as China over the continued detention of Yang Hengjun, North Korea over the now-released Alek Sigley, and Thailand over Hakeem al-Araibi, also now freed.

Australians need to abide by the laws of the countries which they visit Scott Morrison

Australia’s public advocacy on Chau’s behalf has been subdued in comparison. In Hanoi in August, prime minister Morrison was asked directly about Chau’s case, and Australian government overtures on his behalf.

Facebook Twitter Pinterest Chau Van Kham’s family fear his prison term is effectively a death sentence for the elderly man. Photograph: Jessica Hromas/The Guardian

“Australians need to abide by the laws of the countries which they visit,” he said. “They don’t get a leave pass from laws when they go into someone else’s country and commit crimes … but we will always seek to support our citizens in these difficult circumstances.”

Chau’s arrest comes at a delicate moment for Australian relations in south-east Asia. With Chinese relations enduring acute and prolonged strain, and with a growing sense of a diminishing US influence and capacity across the Asia Pacific, Australia is seeking to buttress its relationships with regional countries, in particular allies like Vietnam.

Australia signed a strategic partnership with Vietnam in 2018, particularly focused on defence cooperation, and this year agreed to host annual leaders’ meetings.

Pearson has urged the government to put the rights of an Australian citizen above political concerns.

“Australia should not tolerate Vietnam’s systemic abuses of rights for the sake of prosperity and stability.”

Chau’s wife only wants to hold her husband at home once more.

“It’s too long. Too much pain for me. I want to see him again.”