Colum Carroll, aged 40, from Riverstown, Glanmire, Co Cork, was found collapsed in his single cell in the early hours of August 30 last year. He was taken to the Mater Hospital where he was pronounced dead shortly after arrival.

He was serving a 16-year jail term for possession of €4.5m worth of ecstasy and cocaine.

At Dublin Coroner’s Court, the inquest into his death heard that prison officer Sean Brennan became concerned for him after seeing him slumped over in his third floor cell at around 12.30am.

Carroll had earlier spoken to another inmate, Francis Sherlock, who was on cleaning duty after general lock up. He called him to his cell door and asked Sherlock if he had any “skins” meaning cigarette papers. Sherlock said he got him some and pushed them under the door.

“He seemed okay at this time, his usual self. He was, generally, a happy person. He said ‘Nice one kid, see you in the morning’, giving me the thumbs up. He was smiling at the time,” he told the inquest.

The alarm was raised after PO Brennan saw Carroll and went to request the masterkey to gain access to his cell so he could check on him. This involved going to a centrally located office on the ground floor to get the key, the court heard.

Supervising officer Patrick Moran said he issued the key and PO Brennan subsequently contacted him by radio to say that Carroll was not responding. The emergency services were called. When SO Moran went to the cell he saw Carroll lying on the floor with a nurse officer and another prison officer administering CPR.

Nurse officer Philip Byrne said he went to assist and when he checked for a pulse, there was none. Asked if they had administered heroin antidote Naloxone, he said they hadn’t.

“We didn’t know it was a drug overdose. He wasn’t breathing and there was no heart rhythm,” he said.

The court heard that burnt tinfoil and a small packet of brown powder was found in his cell after his death.

The postmortem exam was carried out by deputy state pathologist Dr Michael Curtis. He said there was no evidence of injury or assault. The main autopsy findings were acutely congested lungs and moderate fatty degeneration of the liver. The liver disease had no clinical significance, he said.

A toxicology screen found the breakdown products of heroin in Carroll’s system. Dr Curtis told the inquest, as well as a “fairly high dose of” of Xanax “just short of the toxic range”, a number of sedatives, paracetamol and sleeping tablet Zopiclone. He gave the cause of death as heroin intoxication and said it was not “dose related”.