KILLER brothers Warren and Jeffrey Dumbrell told a prison officer: "If we go down we're bringing a prison officer down with us."
The pair issued the threat earlier last week, before they were jailed for life for killing Christopher Cawley as his terrified wife and two children looked on in horror.
Warren has been sent to the Midlands Prison in Portlaoise to serve his sentence. He has a history of serious violence against prison officers.
He has also been separated from his brother Jeffrey who is serving the initial period of his life sentence at Wheatfield Prison.
The chilling threat was issued to a prison officer before a jury unanimously convicted Jeffrey of murder and his brother Warren by a 10-2 majority last week.
A source said: "The comment was made as the brothers were being taken from the courts building. They obviously felt things were going against them."
Warren (36) and Jeffrey Dumbrell (30) of Emmett Road, Inchicore had denied murdering Christopher Cawley (33) outside his home at the Tyrone Place flats in Inchicore in October 2006.
The victim was stabbed six times in the back, leg and hip and left to bleed to death as his wife and two of his children looked on in horror.
Warren and Jeffrey Dumbrell were convicted of the murder last week, following a retrial.
The Herald can reveal that, as the Cawley family left the court last Tuesday evening, another Dumbrell brother, Leonard verbally abused them.
In the aftermath of Tuesday's decision, a low-key garda presence was put in place in the Tyrone Place and Emmett Road area of Inchicore, for fear of recriminations.
But there have been no incidents since the conviction.
Prison sources have told the Herald they are not relishing the prospect of being charged with monitoring the brothers.
Warren received a 10-year sentence for starting a riot in Mountjoy Prison in 1997 in which he held five prison officers hostage and threatened them with blood-filled syringes.
When Warren later stood trial over the siege, the court heard that he told prison officers: "I have the virus since I was 15 years old. I don't give a f**k. I'll make you drink my blood."
He also threatened to kill the prison officers, telling their superiors: "You have 10 minutes and you'll be done. I'll do one more every 20 minutes."
At the murder trial the Dumbrells claimed that they only went to Tyrone Place on the night of the killing to confront Mr Cawley, give him "a few slaps" and tell him to leave their brother Tommy alone.