Confronting footage of an Aboriginal man being held down by five police officers before his death has been released.

David Dungay, 26, died behind bars at Sydney's Long Bay jail in December 2015 after he was restrained and given a powerful sedative.

His family have been pushing for footage of the incident to be released, and it was played before a Sydney court during a coronial inquest on Monday.

Confronting footage of a diabetic man being held down by five police officers before his death has been released

David Dungay, 26, died behind bars at Sydney's Long Bay jail in December 2015 after he was restrained and given a powerful sedative

His family have been pushing for footage of the incident to be released, and it was played before a Sydney court during a coronial inquest on Monday

It shows at least five Immediate Action Team prison officers restraining Dungay before he is given an intramuscular injection.

The court heard Dungay was being held at the hospital section of Long Bay Prison after he was diagnosed with mental health issues.

The officers ask Dungay, a diabetic, to place his hands through a gap in the door to be handcuffed before he is moved from his cell, but he refuses.

'Do that now or force may be used,' an officer says to Dungay.

'One, two, three, go, go, go,' an officer says as his colleagues open the door and enter the cell, restraining Dungay.

Dungay is forcefully held down on a bed by four officers, whose faces are blurred in the video.

The prisoner can be heard struggling as he is held down. 'Stop resisting,' an officer says multiple times to Dungay.

'I can't breathe,' Dungay can be heard saying, in between screams as the officers continue to hold him.

Dungay is moved off the bed, and again says that he can't breathe.

He is carried into another cell, where is told he will be placed on another bed.

Dungay is held face down on the bed as a nurse comes into the room and administers an injection.

It shows at least five Immediate Action Team prison officers restraining Dungay before he is given an intramuscular injection

'The more talking you're doing, the more breathing you're doing,' an officer says to Dungay.

'I can't breathe,' Dungay says, to which an officer replies: 'If you're talking, you can breathe'.

The footage was released by NSW Corrective Services, who had argued that revealing the video would expose internal policies including officer weapons, door locks and staff identities.

Counsel assisting the Coroner Jason Downing had previously described the footage as being 'quite graphic'.

Dungay was sentenced to nine-and-a-half years in 2009 for a series of crimes including attempted rape, assault of his girlfriend and violent robbery.

Dungay is held face down on the bed as a nurse comes into the room and administers an injection

The indigenous man, who was three weeks away from being released on parole, allegedly became aggressive towards prison officers when he was ordered to stop eating biscuits.

'It's straight out murder. They murdered my son. They've got to be accountable for it,' Dungay's mother Leetona told the ABC.

Mr Downing said Dungay's cause of death was 'unascertained' according to an autopsy report, the Sydney Morning Herald reported.

'It would appear that Mr Dungay had a cardiac arrest as a result of being restrained in the prone position by the IAT members,' he said.

A NSW Corrective Services spokesperson told Daily Mail Australia they 'deeply regret the death of Mr Dunday'.

'We support the coronial investigation and have co-operated fully with the Coroner.

'Serious consideration will be given to any coronial recommendations addressed to the Commissioner of Corrective Services NSW. The investigation report into Mr Dungay’s death resulted in many changes to policy and training procedures.

'Extensive consultation occurred between Custodial Corrections, Security and Intelligence and Justice Health in relation to policies and procedures relating to the use of force on inmates.

'Sections of the Operations Procedure Manual were reviewed and changes were incorporated into a new Custodial Corrections Policy and Procedure.

'These changes are also now included in all training materials for new and existing correctional officers and were issued as urgent advice to all custodial staff.'