Australia does not control the controversial Nauru detention camp and a Bangladeshi mother and baby who are "terrified" of being returned there would be free to come and go, the High Court has heard. 
The assertion was made by lawyers for the Commonwealth on the second day of the challenge to the lawfulness of Australian-funded detention centres at Nauru and Manus Island, which argues the federal government does not have the power under the constitution to detain people overseas.
The plaintiff is a woman from Bangladesh who was brought to Australia from Nauru in   August last year for medical treatment. Her daughter is now 10 months old and supporters say the mother is "terrified" of returning to Nauru.
On Thursday, counsel for the Commonwealth Justin Gleeson, SC, told the court the centre operates at the will of the Nauruan government and Australia helps the republic to "carry out its law on its soil". He rejected suggestions made by the woman's lawyers on Wednesday that a Nauruan operations manager was involved only at the "helicopter level" at the centre, saying the official was responsible for day-to-day running.
"Everything traces back to the operations manager," he said.
Australia funds the centre and contracts Transfield Services and Wilson Security to operate and secure it, but those firms played only a support role, Mr Gleeson said.
The woman's lawyer, Ron Merkel, QC, told the court on Wednesday that, through a contract with Transfield Services, the Commonwealth funds, controls and implements the powers of detention.
Federal government actions such as asking Nauru to establish the camp, procuring a perimeter fence and applying and paying for visas that require people to be detained showed the camp was an Australian venture, he said.
This week, the Nauru government announced the detention camp would become an "open centre" 24 hours a day, and detainees would be free to come and go as they pleased. On Thursday, Mr Gleeson told the court this meant the detainees are no longer required to remain inside the centre, but may simply use it as a place of residence.