A prisoner told jail bosses he felt safe just hours before he was attacked and left fighting for his life.
Robert O’Connor, 34, had stopped breathing and was revived after the assault in his cell in Dublin’s Mountjoy Prison on Friday evening.
The four men suspected to have beaten him are now in isolation and could be removed for questioning.
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The shocking attack stems from a personal grudge over an alleged assault on the outside.
A prison source said: “He is in a bad way. He is in intensive care and is critical. When he was being attended to by emergency services he had actually stopped breathing.”
O’Connor, from Darndale in North Co Dublin, was handed a six-and-a-half year jail term last Wednesday for possession of a semi-automatic gun in October.
Irish Prison Service bosses carried out a “protection assessment” to establish how safe it was for him to mix with the general prison population.
O’Connor was asked if he felt safe and he told them he did but hours later he was brutally assaulted. One of the suspects is a dangerous member of the Kinahan gang serving a sentence in connection with an attempted murder of a Hutch associate.
He was also arrested in connection with a gangland murder last year.
Another one of the suspects is serving time for a spate of robberies.
Sources said prison bosses immediately sealed off the cell while the suspects’ clothing has been seized by gardai. CCTV footage will be handed over to gardai.
The four suspects were last night being kept alone in separate cells while prison bosses expect that gardai may make an application to remove them for questioning over the next number of days.
An Irish Prison Service spokesman said: “We can confirm a prisoner was seriously injured in Mountjoy Prison. The matter is subject to a Garda investigation.”
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