According to a NSW Health Department report seen by the ABC, the death of 26-year-old Dunghutti man David Dungay Jnr occurred shortly after he was sedated by staff at Sydney's Long Bay prison.
Mr Dungay died on December 29, 2015 shortly after telling prison staff he could not breathe.
The documents reportedly outline the series of events in the lead up to Mr Dungay's death.
Mr Dungay, a diabetic, was ordered to stop eating biscuits. He was ordered to be moved to a new cell with CCTV cameras. Mr Dungay resisted saying he could not breathe. He was told by Corrective Services staff that 'if you can talk, you can breathe'.
In the new cell, Mr Dungay was held down and sedated. He then stopped breathing, and revival attempts were unsuccessful. The documents reportedly state that nursing staff cleaned blood from the cell before police arrived to investigate the death.
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Major failings were outlined in the report, according the to ABC - including a thorough assessment of the health of the patient before administering the drug, emergency resuscitation material not being on had, and the antidote for the sedative not being on hand as is mandated.
Mr Dungay's mother Leetona Dungay told the SMH she believes her son was murdered.
"Straight out murder. They murdered my son.
"They've got to be accountable for it."
Mr Dungay's family is being represented by George Newhouse who told the SMH the family are hoping the inquest, for which no date has been set, will see further questions answered.
"As to any other court process, it's too early to say as yet."
In January, Mr Dungay's family told NITV: “Our hearts are broken and we are grieving his untimely loss.”
“He was not perfect, but we loved him deeply and were so excited about having him back with us."
