The Papua New Guineans charged with his wilful murder are expected to face a court hearing this week on Manus.
There is little sign the two expats will be returned to face the justice process.
The skull of Iranian asylum seeker Reza Barati was fatally smashed in a brutal confrontation in the detention centre on 17 February 2014 that left dozens of detainees and staff injured.
Mr Barati was allegedly assaulted by about ten workers and guards.
Two expats allegedly involved left Manus and Papua New Guinea shortly afterwards.
“That is the point we are still struggling on, having to get these two guys back here and face their charges as well,” Manus provincial police commander Alex Ndrasal said told SBS World News.
Two Manus islanders, employed by then centre operator G4S and the Salvation Army, face wilful murder trials.
The police investigation found, “two expatriate security guards known as (NAME WITHHELD) and (NAME WITHHELD) also assisted in beating the bleeding deceased whilst he was lying on the balcony floor."
“We know the first names, the second names is the struggling issue we are trying to find out,” said commander Ndrasal.
“The previous management probably didn't co-operate very well with the police to speed it up and that is the reason why we cannot bring them back immediately.”
G4S says it has not had a request from police regarding the expats and supports “the full and proper application of PNG law … and continues to cooperate fully with the PNG police investigation”.
Papua New Guinea has accused Australia of repeatedly breached its sovereignty by removing suspects in cases on Manus before police can interview them.
Rape and drink driving investigations on Manus are stalled due to the absence of expats allegedly involved.
“How would you feel if Papua New Guineans caused offences in the same way in Australia and evacuated them on the same day?” PNG prime minister Peter O’Neill said.
“We have to respect each others laws.”
The murder trial of the two locals is listed for this week on Manus but is expected to be deferred.
