The sister of a man killed by Michael Stone said she fears the newly-released loyalist killer will come after her family.
Lawyers acting for Deborah McGuinness are on Thursday set to challenge the decision to release him on parole.
An emergency judicial review has been issued over the legality of the Parole Commissioners' decision to free Stone from Maghaberry this week.
Mrs McGuinness told the Belfast Telegraph that she still lives in fear of Stone.
One of Northern Ireland's most notorious terrorists, he killed three people including Mrs McGuinness' brother Thomas McErlean at Milltown Cemetery in 1988.
He was also responsible for the earlier murders of three Catholic men in separate attacks.
He was not due for release until 2024, having failed in an earlier parole bid, but it emerged on Tuesday night that he was out.
According to her solicitor, the challenge, to be heard in Belfast's High Court on Thursday morning, will also address the decision of the commissioners not to provide reasons for their decision to release Stone, their refusal to provide documents or information about the proceedings, or allow the relatives of his victims to participate.
Paul Farrell, who is acting for Mrs McGuinness, said: "This case is of huge importance, not only to the victims of Michael Stone and their families, but also it will have huge ramifications with regard to the future of parole hearings in Northern Ireland."
Mr McErlean (20), a Catholic from west Belfast, was among three people killed by Stone in the gun and grenade attack at Milltown.
Another civilian, John Murray (26), and IRA member Kevin Brady (30) also died.
Mrs McGuinness said news of the freedom brought her back to his first release in 2000 under the terms of the Good Friday Agreement.
Stone was returned to prison after entering Stormont in 2006 armed with explosives and an axe in an attempt to murder Sinn Fein leaders Gerry Adams and Martin McGuinness.
Mrs McGuinness said the families of Stone's victims want inquiries into their murders to examine suspicions of security force collusion.
"We want our truth. He's been out twice and we're still fighting for an inquest," she said.
"We're getting the information like ordinary people and reading it in the papers."
She said she is afraid Stone will approach her family, adding: "He's a serial killer. Nobody knew what he was capable of the last time, so who is to say he wouldn't come to my door?"
She received a phone call from police on Tuesday to tell her Stone would be released within seven days.
He was freed that same night and Mrs McGuinness found out while watching the news.
She added: "My brother was an innocent victim. He was only 20 and he was married with two sons. He had a daughter he never met. His children are in their 30s now.
"My mother went to her deathbed really still wanting the inquiries to go on.
"We were told the day he died that we wouldn't get an inquest. That's why it's so important to us and his children.
"It will go on until the next generation, so it needs to be sorted and not carried on. We don't want it to go on to a third generation. Like most victims, we're just waiting and it's like being on a roller-coaster.
When it was confirmed in 2019 that Stone would not be released until 2024, Mrs McGuinness said it was "a real relief".
"If you do the crime you should go and do the full amount of time," she said.
The memory of her brother still lives on in his family's minds, she said, and they talk about him "at special moments - at Christmas, at sad times or when his grandchildren are born".
She added: "(My brother) hasn't been there in a long time. It's the families that suffer, let's be honest. We're not going to stop until we get the truth."
Ms McGuinness' solicitor welcomed the ruling as a step towards greater openness in the parole process.
Paul Farrell, of McIvor Farrell law firm, said: "This case is not a persecution of Michael Stone, it was taken by my client to address the potential risks to the public that may arise upon his release.
"However, the issues that arise are common across the whole parole process, where victims have ongoing concerns regarding offenders who are to be resettled in the community."