Australia is responsible.

Dear Prime Minister,

UNHCR renews its call for Australia to urgently find viable, humane solutions outside of Papua New Guinea and Nauru for those remaining under offshore processing arrangements.
— http://www.unhcr.org/news/press/2017/8/598c5ca54/unhcr-warns-escalating-crisis-manus-island.html
George Newhouse says the family want an urgent independent autopsy to determine the cause of death for which PNG police have ruled out foul play.
Meanwhile protests at the detention centre on Manus Island continue with inmates calling for an investigation into the latest death.
”There is a paper trail in this case that leads all the way up the line in Border Force, IHMS [International Health and Medical Services] and in the government, and the family want to know how they could allow their son to remain without proper medical care and in such awful conditions when they knew his vulnerability.” - George Newhouse
— http://www.radionz.co.nz/international/programmes/datelinepacific/audio/201854300/lawyer-aus-govt-to-blame-for-latest-refugee-death-on-manus

End offshore detention and bring all refugees and asylum seekers on Manus Island and Nauru to Australia now.