Manus Island security company GS4 says it is unsure which of its staff was involved in the fatal bashing of Iranian asylum seeker Reza Berati.
Investigations by Papua New Guinea police suspect that three GS4 guards and two local men were responsible.
Mr Berati died from major head injuries during riots at the detention centre in February.
GS4 admits that it hasn’t identified which of its employees are responsible, and had passed all information to PNG police.
GS4 managing director for immigration services Chris Manning said that it was not the role of the company to investigate.
In an interview with the ABC, Mr Manning said that GS4’s role was to support PNG police “to ensure that anybody who has broken the law in this brutal and horrific way is brought to justice.”
A government-commissioned review of the riots has angered PNG police, who are yet to finish their investigation, according to a report by Sky News.
A PNG police spokeman told Sky News that the government had been frustrating their efforts “since day one”.
“We were frustrated by the lack of co-operation by the Australian government, the security service provider G4S and asylum seekers,” a PNG police spokesman told Sky News.