An appeal hearing by four dissident republicans held liable for the Omagh bombing has heard an FBI agent who gave evidence during the case is a "pathological liar".
Michael McKevitt, Liam Campbell, Seamus Daly and Colm Murphy were successfully sued by 12 victims' relatives, who were awarded £1.6m compensation last June.
The men started an appeal procedure on Monday, which is due to last two weeks.
The Court of Appeal heard that an FBI double agent, who gave evidence during the case is a "pathological liar".
Lawyers for Michael McKevitt told the court on today that he would advance 16 grounds of appeal, most of which relate to the evidence of American agent David Rupert.
Mr Rupert's account of his infiltration of the Real IRA was used in the civil action.
But defence counsel Michael O'Higgins said the judge in the civil action had not taken account of defence arguments that Mr Rupert was ''a confidence trickster and a pathological liar".
He said because David Rupert had not given evidence in person, the trial judge had not been able to hear the direct evidence and lawyers for Michael McKevitt had not been able to cross-examine Mr Rupert.
Mr O'Higgins said the evidence was circumstantial, the findings of the court were tainted and the end result was flawed.
The latest legal challenge over the case at the Court of Appeal could last up to two weeks.