An asylum seeker who had been suffering acute mental health crises for more than a year – and whose friends had pleaded with Australian authorities for him to be treated – has been found dead on Manus Island.

The body of Hamed Shamshiripour, an Iranian national, was found in the forest near the Australian-run East Lorengau refugee transit centre. Manus province police chief, Inspector David Yapu, confirmed the death and said a crime scene had been established.

The Guardian has seen photographs, purporting to show Shamshiripour as he was found in the forest. The body has visible wounds, but the circumstances of his death are unclear.

The initial reported cause of his death, suicide, has been contested by refugees and asylum seekers on the island. There are reports from Manus island that Shamshiripour had been missing since Saturday.

Shamshiripour, 31, had initially been rejected for refugee status, but that status was being reviewed. Several refugees said Shamshiripour had recently made attempts to commit suicide.

Shamshiripour had spent some time in Australia for medical treatment.

The Guardian reported in June last year that Shamshiripour was found, naked in the Mike compound, yelling in an incoherent and distressed state, and was arrested and taken to Lorengau prison, before being taken to the “managed accommodation area” within the detention centre for people suffering mental health problems.

According to a formal complaint made by 14 fellow refugees and asylum seekers, Shamshiripour was beaten by guards instead of being cared for.

“We, the signatories to this complaint form want to know why you are not providing mental health support to Hamed … and instead you have subjected him to ill-treatment and corporal punishment because he is not behaving normally due to his mental ailment.”

A letter of complaint to the Manus Island detention centre over the treatment of Iranian asylum seeker Hamed Shamshiripour

In January this year, Shamshiripour was jailed again following an acute mental breakdown. He was released from prison, only to be found wandering the streets of Lorengau half-naked, “hungry and homeless” according to refugees, police and politicians on the island.

Leaked psychological support files from within the Manus Island detention centre refer consistently to Shamshiripour’s “chaotic presentation” and report he was “agitated, aggressive, verbally abusive, pushing boundaries constantly, and has required police presence on numerous occasions”.

Another report says: “Hamed is currently acting erratic, raising serious mental health concerns, and not engaging in linear discussions with case managers or others. Hamed’s behaviour prevents a cooperative, meaningful engagement and report based on observations.

“Hamed informed case manager he has not made a decision about returning to Iran (while he was singing he said I want to go to Iran, wants to go to Persia). He has become a danger to stakeholders and residents alike with his erratic and unpredictable behaviour.”

In other reports, Shamshiripour was seen by staff drinking local home-brew alcohol and was warned of its dangers.

Shamshiripour was jailed several times after suffering severe mental episodes and behaving unpredictably or aggressively. Detention centre staff told Guardian Australia he was “a very sick man. He needs serious help.”

In January Manus MP Ron Knight, who arranged for Shamshiripour to be released from prison so he could access mental healthcare, said he was receiving none.

“To be blunt, the guy is dangerous to all around him and he needs psychiatric help. There is none for him here.”

Knight said he approached the Australian high commission in Port Moresby about Shamshiripour being committed to a psychiatric facility.

“The response to me was basically that our authorities should handle it.”

Australia’s Department of Immigration and Border Protection, which runs the detention centre and the refugee transit centre on Monday confirmed it was “aware of a death in Lorengau township”.

“PNG authorities are investigating the matter.

“Further questions should be directed to the government of PNG.”

Shamshiripour’s family has been informed of his death.

Five refugees and asylum seekers have died on Manus Island under Australian government control since offshore processing was restarted in 2012.

Ian Rintoul from the Refugee Action Coalition said while suicide was supected in Shamshiripour’s death, refugees on Manus were convinced his death was suspicious as he had been targeted for violence in the community.

Rintoul said Shamshiripour’s death confirmed the worst fears of refugees who are currently being coerced to leave the detention centre for the transit centre where Shamshiripour was held.

“Manus is not safe. East Lorengau is not safe. They have already told border force that they will not move.”

Amnesty International’s Graham Thom said Shamshiripour’s death was “yet another bleak tragedy to arise out of the ongoing suffering and tensions on Manus Island”.

“It is not yet clear if his death was a result of self-harm or violence. Irrespective of the cause, Australia must accept liability for the damage its cruel policies are causing refugees.

“This was a man who came seeking Australia’s protection, Amnesty International is gravely concerned that he was provided inadequate healthcare and that his safety was not the paramount consideration.”

• In Australia, the crisis support service Lifeline is on 13 11 14. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. In the UK, the Samaritans can be contacted on 116 123. Hotlines in other countries can be found here