Two men held liable for the Omagh bombing are seeking to go before the European Court of Human Rights to overturn the ruling, it has emerged.
The pair are jailed Real IRA leader Michael McKevitt and Liam Campbell.
Lawyers for the two men have based the challenge on their inability to cross-examine an FBI spy whose evidence was central to the case against them.
The disclosure comes as two other men originally held responsible prepare to face a retrial at Belfast High Court.
No-one has ever been convicted of carrying out the 1998 Omagh bombing, but in 2009 McKevitt, Campbell, Colm Murphy and Seamus Daly were all held liable for the bombing in a civil ruling.
The Court of Appeal subsequently upheld Mr Murphy and Mr Daly's challenges to the verdict and ordered them to face a retrial, which gets under way next week.
However, McKevitt and Campbell failed to overturn the rulings against them.
Legal papers prepared on their behalf focus on the role and credibility of David Rupert, an American trucking boss-turned FBI spy who infiltrated dissident republican ranks, and is now on a witness protection programme.
Although Rupert was forbidden from attending the original civil action for health and security reasons, more than 900 emails between the spy and his handlers were submitted as evidence.
Kevin Winters, the lawyer representing McKevitt and Campbell told the BBC that the European Court Court of Human Rights will be asked to consider the reliance on the hearsay evidence of David Rupert and the inability to cross-examine him about his claims."
A provisional ruling on the merits of the application by July.