A man who tried to kill a teenager who was camping with friends at a Dublin beauty spot has attempted to slash a prison officer's throat.
Michael Corbett (30), who is serving nine years for attempted murder, previously attacked another inmate with a hot kettle and tried to strangle a psychiatric nurse with a sock.
On Monday evening, Corbett, who had been released from his cell in the High Support Unit in Mountjoy, tried to slash the officer's neck with a shiv - a blade melted into a toothbrush.
Thanks to the officer and a colleague's quick actions, Corbett was subdued and the officer was taken to safety.
A source said the incident was "as bad as it gets".
"This was pre-planned and vicious. There was absolutely no history between him and the officer," they said.
"The officer just unlocked his cell after tea for recreation time and Corbett came straight out and tried to slice his throat.
"There were no words exchanged between them.
"It was the quick actions of this officer that saved him. He could very easily have been killed.
"The threat posed by Corbett is massive. Many in the prison are convinced he intends to kill someone. It's only a matter of time."
In July, the Central Criminal Court ruled that six years of the suspended portion of Corbett's attempted murder sentence be reactivated for repeated violent attacks in custody.
Mr Justice Michael White said a psychiatric report on Corbett showed he is at risk of future violence.
"It is a situation that will confront society again when Mr Corbett is released," he said.
He added that a comprehensive psychiatric report detailed Corbett's substance abuse while in custody and his history of violence toward his carers and fellow inmates.
The judge said he was particularly concerned that the report stated Corbett is at risk of not adhering to treatment for his psychotic illness when he is released.
Mr Justice White said he did not want to use prison "as a repository for people with serious psychiatric or psychotic problems" and that the risks in this case were such that he had to take a " very serious view of the behaviour of Mr Corbett".
Father-of-one Corbett, who had a previous address in Raheny, was living rough when he assaulted his 17-year-old victim on June 27, 2016, at the Hellfire Club on Montpellier Hill.
The teenager suffered a four-inch stab wound to the chest.
Corbett also attacked two of his friends, hitting one with a plank of wood around the head.
He was committed to the Central Mental Hospital (CMH). While there, he attacked nurse Declan Curtin on October 6, 2016.
Staff were escorting Corbett to an exercise period when he asked to use the toilet.
When Mr Curtin went in after him, Corbett used a sock to try to strangle him. He managed to free himself, but has suffered flashbacks and anxiety since the assault.
Judge Melanie Greally, at Dublin Circuit Court, imposed a five-year sentence on Corbett and suspended the final two-and-a-half years for 15 years on strict conditions.
As the custodial portion of his attempted murder sentence came to an end in July 2018, he remained in custody for the assault on the nurse.
A spokesperson for the Irish Prison Service said Monday's incident has been referred to gardaí.