David Dungay Jnr, 26, died at the Long Bay Correctional Complex in Matraville on December 29.

The ABC's PM radio program reported on Thursday that Mr Dungay was eating a packet of biscuits in the jail's hospital complex and was told by prison guards to stop doing so.

Citing a leaked report from the NSW Health Department, the program said Mr Dungay, who had diabetes and schizophrenia, became "combative" and refused.

As a result, the jail's riot squad attempted to move him to a cell with CCTV cameras so he could be monitored. However, he resisted, saying he couldn't breathe.

Officers reportedly responded that if he could talk he could breathe, before escorting him to the cell and holding him face-down on a mattress.

Mr Dungay was then injected with the sedative midazolam, the ABC reported, citing an autopsy report which was also leaked. Soon after, his face turned purple and he stopped breathing.

His airway, pulse and vital signs were reportedly not checked before the sedative was administered as they should have been.

Lawyer George Newhouse, who is representing the Dungay family ahead of a coronial inquest into Mr Dungay's death, told Fairfax Media they remained emotional about their loss.

"As you can imagine, the loss of a loved one stirs up high emotions," he said. "In my opinion they are still shocked and grieving the loss of their loved one."

Mr Newhouse said the family would pursue the inquest in the Coroner's Court in the hope of getting some answers, but it was too early to say if further court action would follow.

"The family are hoping to find the truth about their son's death," he said. "They want anyone responsible for his death to be held accountable, and they want changes made in the healthcare system and in the way cell extractions are undertaken to make sure no one ever dies in this way again.

"As to any other court process, it's too early to say as yet."

In a statement following the program, Corrective Services NSW said staff had met with Mr Dungay's family and continued to liaise with them as a "thorough investigation" was being conducted into his death.

"Corrective Services NSW Commissioner Peter Severin deeply regrets the death of inmate David Dungay at Long Bay Hospital, in the Long Bay Correctional Complex, on 29 December 2015," a Corrective Services spokesperson said.

The CSNSW Investigation Unit, which includes members of the NSW Police Force, has been conducting a thorough investigation into Mr Dungay's death. Preliminary indications suggest there was no criminal negligence.

"As the death is still before the NSW Coroner, further comment cannot be made at this stage."

No date has been set for the inquest. It is expected hearings will not begin for at least a year.