Loyalist killer Michael Stone has been released from prison on parole, BBC News NI understands.
One of the most notorious paramilitaries of the Troubles, he killed three people in an attack at Milltown cemetery in 1988.
It was taken by families of his victims in an attempt to delay his release.
They have been informed of the move.
It is understood Parole Commissioners took the decision on Monday and he was freed from Maghaberry Prison on Tuesday.
Before now, he had not been due for release until 2024, having failed in an earlier parole bid.
After being freed under the Good Friday Agreement, he was sent back to prison after entering Stormont armed with explosives and an axe in an attempt to murder Gerry Adams and Martin McGuinness.
Families of the Milltown victims had taken legal action, arguing he was not entitled to another parole attempt, but the court found against them.
That paved the way for a second, and successful, attempt at parole.
Thomas McErlean , 20, was one of those killed during that attack on Milltown cemetery.
His family are calling for "a proper investigation into his death".
In a statement, the McErlean family said it was "unjust Michael Stone is able to move forward with his life when he took the lives of Thomas McErlean and many other people".
As well as the Milltown cemetery murders, he was convicted of three other killings.
Stone's other victims were:
- Milkman Patrick Brady, who was murdered in south Belfast in 1984
- Joiner Kevin McPolin, who was shot in the head in Lisburn, County Antrim, in 1985
- Bread delivery driver Dermott Hackett, who was shot up to 16 times with a submachine gun in his work van in 1987
In a statement the family of Dermot Hackett said they still live with "the heartache caused by the murder of their husband and father, son and brother" and that "not a day goes past without them thinking of him".
In 2006, he entered Parliament Buildings at Stormont, armed with explosives and an axe, in an attempt to murder Sinn Féin leaders Gerry Adams and Martin McGuinness.
Stone denied it had been a bid to kill the politicians, instead claiming it was "an act of performance art".