Relatives of Omagh bomb victims are suing Northern Ireland's police chief over investigative failings they believe let the killers escape justice.
The writ against Police Service of Northern Ireland (PSNI) chief constable George Hamilton focuses on what happened after the bomb detonated on August 15, 1998 and why, 19 years on, no one has been convicted in a criminal court.
The relatives' solicitor said "delays in arresting known suspects by the police" was a particular concern.
The Real IRA bombing killed 29 people, the greatest loss of life of any terror atrocity in the history of the Northern Ireland Troubles.
Families of the victims are seeking damages and a declaration their human rights have been breached.
The PSNI said it would "take time to consider the contents and respond in due course" once it received the writ.
It is the latest legal twist in the families' two-decade quest for justice and answers.
They are pursuing judicial review proceedings against the 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, and 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.
The writ cites the damning findings of official inquiries and court proceedings that identified multiple failures in how police investigated the bombing, including:
- 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
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 said.
Stanley McComb, whose wife Ann was killed, said: "Every morning I waken I am on my own, every night I go to bed I am on my own.
"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."
Next week will be the 19th anniversary of the bombing, which claimed the lives of people 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.