Repairs to the Christmas Island immigration detention centre after last November's riot won't be finished until July at a total cost of $7.65 million.
A group of detainees went on a rampage in the centre after the death of Iranian Kurdish asylum seeker and centre escapee Fazel Chegeni.
The centre was set alight and security guards fled before the federal police raided the compound, injuring five detainees.
The extensive repair bill was initially estimated to be around $10 million.
But the Department of Immigration and Border Protection now says although the repairs remain ongoing, the expected cost has declined.
The department told AAP in a statement "work will be completed by July 2016" with most repairs being done on education facilities.
So far, $3.4 million has been spent, with the final cost anticipated to be $7.65 million.
After the riots a number of detainees were moved from the island to prisons in Western Australia.
At the time, Immigration Minister Peter Dutton said detainees found to have damaged Commonwealth property would face "the full force of the law".
However, the AFP won't say if any charges have been laid, or if criminal charges are still being considered.
"This matter is an ongoing investigation. As such it would not be appropriate for the AFP to comment at this time," a spokesman said.
