Relatives of Omagh bomb victims are to sue Northern Ireland's police chief for investigative failings they believe let the killers escape justice.
Ahead of next week's 19th anniversary of the Real IRA outrage that claimed the lives of 29 people, bereaved families have issued a writ against Police Service of Northern Ireland chief constable George Hamilton seeking damages and a declaration their human rights have been breached.
It is the latest legal twist in their two-decade quest for justice and answers.
The families are pursuing judicial review proceedings against the British Government's decision not to hold a public inquiry into claims the attack could have been prevented if it had not been for a series of intelligence failings.
The writ against Mr Hamilton focuses on what happened after the bomb detonated on August 15 1998 and why, 19 years on, no one has been successfully convicted in a criminal court.
The relatives have already successfully sued four republicans in a landmark civil trial that found they were responsible for the bombing.
The latest court action has been issued against Mr Hamilton because he has legal responsibility for the actions of both his service and its predecessor, the Royal Ulster Constabulary.
Michael Gallagher, whose 21-year-old son Aiden died in the bomb, said the families needed answers.
"Here we are 19 years on and the criminals responsible for this are still walking the streets - there has been absolutely no punitive measures taken against any of them," he told the Press Association.
He added: "We can't walk away and say 'it's just one of those things'.
"In our case it wasn't just Aiden that died, all of us died that day, our lives have never been the same and we need some answers."
Stanley McComb, whose wife Ann was killed, explained his motivation.
"Every morning I waken I am on my own, every night I go to bed I am on my own," he said.
"My partner, my wife of 25 years, is no longer there and should be there. It does hurt you, you learn to live with it, but that's what drives me on.
"Why should people get away with something like that? If I broke the law or anyone decent breaks the law they are punished for it, and these people came in and murdered my wife in this town and it drives me on, there's no way I am giving up."
The action is issued in Mr Gallagher's name on behalf of bereaved families belonging to the Omagh Support and Self Help Group.
It cites the damning findings of official inquiries and court proceedings that identified multiple failures in how police investigated the bombing.
These include -
:: a 2001 report by Police Ombudsman Nuala O'Loan found many evidential opportunities were missed and expressed concern that warnings of a likely attack passed to police by informants were not acted upon.
:: acquitting south Armagh electrician Sean Hoey of the Omagh murders in 2007, trial judge Mr Justice Weir heavily criticised the way forensic evidence had been dealt with.
:: a 2014 report by Police Ombudsman Dr Michael Maguire highlighted inexplicable delays in arresting known suspects in the days after the attack. He also found that key intelligence was not disseminated from RUC Special Branch to detectives on the ground.
:: fatal flaws in state evidence exposed when the prosecution of South Armagh bricklayer Seamus Daly for the Omagh murders was dropped before it reached trial last year.
The Omagh bombing inflicted the greatest loss of life of any terror atrocity in the history of the Troubles.
The dead came from both sides of the Irish border, England and Spain. One of the victims was pregnant with twins.
Relatives will gather at a memorial garden in Omagh on Sunday for their annual service of remembrance ahead of Tuesday's anniversary.
The relatives' solicitor John Fox explained the basis of the latest legal bid.
"A particular concern is the delays in arresting known suspects by the police and the families have tried to get answers from the PSNI and the public prosecution (service) and have yet to get any answers to the questions that remain unanswered," he said.
"And that is what they are now bringing before the court - an action against the chief constable of the PSNI to get answers in relation to how the police investigation was handled."
In response to the sending of the writ, a PSNI spokeswoman said: "Once received, we will take time to consider the contents and respond in due course."
Asked about the legal action, Will Kerr, a former assistant chief constable with the PSNI, now a director at the National Crime Agency in London, said: "Obviously I have complete sympathy and concern for the families of the Omagh bombing but that's not something I can comment on. That's for the Police Service of Northern Ireland to comment on."