But Mr O'Connor's cellmate, one person who might have been able to shed more light on the inmate's last moments, on Wednesday denied any knowledge of what drugs the man may have taken.

The 29 year old died on May 13, 2017, from a fatal combination of ice, the synthetic opioid buprenorphine and an anti-psychotic, though there was enough ice alone in his system to have killed him.

At the time Mr O'Connor and a cellmate were being locked in their cell for 23 hours a day.

The cellmate was called to give evidence at an inquest into Mr O'Connor's death on Wednesday when he said he was watching television in the cell after their hour outside when he heard a thud.

Mr O'Connor had collapsed, he said, so he pulled the man onto his bed and checked for a pulse, counting two in about 12 seconds.

He said the man's lips started going blue so he blew one or two breaths into his airways before calling for help.

A forensic pathologist has given evidence it was likely that the ice in Mr O'Connor's system had been consumed shortly before the emergency was called at 6.55pm that evening.

But the cellmate denied from the witness box that they had been taking ice.

He denied too any knowledge of the buprenorpine - which can be prescribed but is also popular contraband among prisoners - in Mr O'Connor's system.

He said that sometime after the incident, after police and corrections had searched the cell, he had walked back in to retrieve his things and found a half-fingernail sized rock of ice on the desk.

He said he later smoked the ice in an adjoining cell, and that he did not know where it came from.

Under questioning the detainee denied knowing how the ice found in Mr O'Connor's system came to be there and denied seeing the man consume any drugs.

The witness denied a further incident on May 15, in which a corrections officer reported seeing him pull a syringe out of his arm.

Corrections officers were not able to find the capped syringe when they searched him and the cell, and the detainee denied that he had swallowed it and then vomited it up and flushed it.

The court has heard that various prisoners who had approached Mr O'Connor's cell door in the hours and days before his death had declined to give statements.

One detainee that was called to give evidence is seen on surveillance footage receiving medication from the medical window before placing his hand to his mouth and then his pocket.

He then goes to Mr O'Connor's cell and passes something over the door.

But the inmate denied in court on Wednesday memory of the day.

"I don't divert my meds ... I wouldn't have done it."

Coroner Glenn Theakston will hand down his findings at a later date.