Medical reports obtained by the Herald on Sunday reveal Akuhata was assaulted in his cell about 3.30pm on November 25.
Prison staff failed to notice he had been assaulted until the next day when they took him to hospital. The report states Akuhata was "found to be semiconscious this morning" and once taken to Auckland City Hospital was lying in bed unable to open his eyes or talk.
Akuhata was examined by doctors about 9pm on November 26, almost 30 hours after the attack, and was bruised on his face and body and "comatose".
His lawyer, Richard Francois, said Akuhata was treated at a rehabilitation centre before he was returned to the prison. He is now at Auckland Prison, Paremoremo.
Francois said his client was seeking punitive damages against Serco as a claim of criminal negligence could not be successful because of New Zealand's Accident Compensation Act.
"We are bringing a Bill of Rights claim - every prisoner has the right to be treated in a humane manner and not be subjected to cruel, disproportionately severe treatment or torture," he said.
"We are also alleging gross negligence on the part of Serco."
The Department of Corrections said questions over Akuhata would be forwarded to the Chief Inspector who was carrying out "a comprehensive review of incidents, the adequacy of the monitoring and systems that are in place to prevent it happening again".
Serco would not comment on the incident but said it would co-operate with all investigations into alleged incidents at Mt Eden Correctional Facility.
They include claims inmates had been injured after being "dropped" off balconies in the prison, fight clubs, drug taking and the use of banned cellphones by inmates.
On Friday, Corrections Minister Sam Lotu-Iiga announced Corrections would take over the running of the prison.
The Corrections investigations will be completed by the end of August and phase two by the end of September.
