Gardaí investigating a murder in Mountjoy jail have discovered a blood-stained make-shift knife, it emerged today.
A forensic team is also studying blood-stained clothes which have reportedly been recovered from the prison.
Alan Green (30) from Co Wicklow, was serving a nine-month sentence for drugs possession when he was stabbed once in the chest yesterday in his cell on the prison's B-wing.
He was taken to the nearby Mater Hospital where he was pronounced dead less than an hour after the attack.
The murder scene remains sealed off as detectives interview the 100 inmates who had access to the landing when the incident took place.
They must be granted a Section 42 warrant from the District Court before suspects can be arrested from the prison for questioning.
The make-shift knife, known as a "shiv" in prisons, is believed to have been found hidden in a cistern in a toilet area.
Shivs are made from a sharpened piece of metal with tape wrapped around the end to act as a handle.
A post-mortem confirmed that Mr Green died from a single stab wound to the heart.
He was discovered at lunchtime yesterday as prisoners collected their midday meals.
In the two hours directly prior to that there would have been a lot of movement around the prison as inmates received visits or attended classes according to a prison service spokesman.
Mr John Lonergan, the governor of Mountjoy Prison, condemned the murder as an act of brutality and savagery. Mr Lonergan apologised to the man's family and said he accepted the system had failed in its duty of care.
He confirmed that the prison would be conducting its own internal investigation alongside the Garda probe.