During the final Manus inquiry hearing into the fatal violence during February, immigration department representative Mark Cormack confirmed 317 asylum seekers had returned home since last July.

He said the decision to offer increased financial assistance was made at the end of March and implemented two months later.

''The rationale for the increase was really to ensure that there was no barrier to people who had voluntarily put their hands up to return to their country and in some cases, that barrier was support for them to get back in the country and support themselves,'' Mr Cormack said.

Documents presented to the inquiry also show security fencing and lighting on Manus Island have still not been completed, despite being key recommendations made by the commander of Operation Sovereign Borders Lieutenant-General Angus Campbell in October.

As reported by Fairfax Media last month, ''return packages'' range from $3300 to $10,000 based on ''individual circumstances'', compared with Labor's offering of $1500 to $4000. Lebanese asylum seekers are being paid $10,000 if they voluntarily return home, while Iranians and Sudanese are offered $7000, Afghans $4000 and Pakistani, Nepalese and Burmese $3300.

Asylum seekers who take up the offer must spend their own cash before receiving the payment.

''Yes, there are different amounts of assistance in accordance to a calculation that is made to the GDP per capita in the country of return, so there is a sliding scale that is based on that,'' Mr Cormack said. He said he would take the different amounts offered on notice.

Since last July, 245 asylum seekers have voluntarily returned to Iran, 27 to Iraq, 17 to Lebanon, 15 to Vietnam, four to Bangladesh and two each to Pakistan, Sri Lanka and Sudan.

But General Campbell, who was also at the inquiry, was quick to point out that the increased amount of money being offered to the detainees were not to ''encourage return''.

''It's really important to note that these are voluntary returns and the variations are to better reflect the economic conditions of the country,'' he said.

When pushed on the location of the customs vessel carrying 153 asylum seekers, General Campbell refused to comment, saying the matter was before the High Court.

''In regard to that issue, that is a matter under the High Court and I wouldn't be able to answer that.''

The inquiry also heard that security fencing and lighting have still not been completed.

General Campbell's report was received by both the Immigration Department and Immigration Minister Scott Morrison on November 5.

But three months later, as violence erupted in the Papua New Guinea centre that killed one asylum seeker and injured 69 others, not one of those recommended changes had been implemented.