The suspect — a man in his early 30s who is on remand charged with violent robbery — passed internal Irish Prison Service checks for inclusion on an “enhanced regime” which confers privileges on prisoners, including clearance for much sought-after kitchen duty.
Sources said he had been of good behaviour for the past two months.
He was in isolation in the jail’s D-unit last night after the fatal assault, which sources say was “sudden, savage, and brutal”.
Gardaí have launched a murder inquiry.
An autopsy confirmed Graham Johnson, 41, from Ardan, Bandon in West Cork, died from a single stab wound to the chest.
The weapon, believed to be a kitchen knife, could have been up to 30cm long.
It is understood there was an argument among two of a group of up to seven inmates working in the kitchen area of Cork Prison at around 2pm on Saturday about what they were going to watch on TV during their break later.
It is believed one inmate wanted to watch soccer, another horse racing.
The fatal attack happened in the kitchen just before 5pm when a row flared over access to the remote control.
“He [the victim] was a good guy. There was no hassle with him. The attack has left prisoners and staff very upset and shaken,” a source said.
Prison officers were on the scene within seconds. The attacker dropped the weapon and offered no resistance.
Johnson was pronounced dead at the scene, which was sealed off by gardaí for forensic examination.
Johnson was jailed in 2011 for five years, with one suspended, for robbery and larceny. The court heard he was a chronic gambler who stole €15,000 from his employer in 2007, and robbed Hatton’s Goldsmiths, Mallow, in 2011 to feed his addiction.
Prison sources described him as a quiet man who cooperated fully with staff and never caused trouble. He was due for release around this time next year.
The Inspector of Prisons and the Irish Prison Service, which would only confirm that a violent incident had occurred, have launched separate investigations.
The governor of Cork Prison has offered counselling services to the prisoners who witnessed the attack.
Gabriel Keaveny, assistant general secretary of the Prison Officers’ Association, said it underlines the growing problem of knife crime in Irish prisons.
“Ultimately, it’s management who decide where prisoners go and work,” said Mr Keaveny.
“We have told the director general of the prison service that there is a serious issue with knife crime in prisons. And he hasn’t responded sufficiently.”
It is the third death in an Irish jail in recent weeks. An inmate was found dead in his cell at the Midlands Prison in Portlaoise on May 9, a day after another prisoner was found dead in his cell at Mountjoy jail in Dublin.