The unrest at the Manus Island camp in February also left 69 people injured as tensions flared among inmates about their fate under Australia's hardline asylum-seeker policies.
An independent review on behalf of the Australian government found no particular factor caused the violence at a camp that has been condemned as too harsh by the United Nations.
"It is not possible to isolate one factor which, if handled differently, may have resulted in less injuries and damage or to apportion blame for causing the incidents directly to one or more of the parties involved," it said.
There was also antagonism between some in the camp and PNG nationals working there, with some asylum-seekers treating them "in a disrespectful and racist manner".
Manus Island houses one of two remote Pacific camps used by Canberra in its punitive offshore detention policy, the other is on Nauru.
Under the policy, any asylum-seeker arriving by boat is transferred to the centres for processing and permanent resettlement.
