The Sinn Féin president, Mr Gerry Adams, has been ordered, by way of subpoena, to appear before the North's High Court as part of a multi-million pound civil action by relatives of the 29 Omagh bombing victims.
Mr Michael Gallagher, whose son Aidan was killed in the bombing, told The Irish Times last night that republicans had often told him of their desire to help the Omagh families. "Now is their opportunity," he said.
The Mid-Ulster MP, Mr Martin McGuinness, and West Tyrone MP, Mr Pat Doherty, along with Mr Brian Gillen and Mr Brian Keenan - both alleged influential IRA figures - have also been subpoenaed.
Mr Gallagher said the "Real IRA", which bombed Omagh, was a breakaway group from the Provisional IRA.
"I hope the former friends of these people can help tell the story of Omagh," he added.
The High Court action is due to start later this year when relatives of some of the 29 victims seek £10 million compensation from the gang which they blame for the August 1998 outrage.
Mr Michael McKevitt, allegedly a former quartermaster general of the Provisional IRA, is one of the five "Real IRA" suspects being sued by the relatives in a civil action begun last month.
Mr Adams has repeatedly denied membership of the Provisional IRA, but lawyers and the Omagh relatives believe he and the others could provide vital information about republican strategy at the time Mr McKevitt quit in a bitter row over Sinn Féin's involvement in the developing peace process.
A spokesman for Mr Adams last night said he had not been made aware of the court summons. He added: "We do not want to comment until we have found out the detail of that."
Mr McKevitt (51), who is currently on remand in Portlaoise prison and facing charges of directing terrorism, has been named in court papers as an alleged "Real IRA" member along with Liam Campbell (38), who is serving a sentence in Portlaoise for membership of an illegal organisation.
Also named are Colm Murphy (51), the only person convicted so far in connection with the Omagh bomb, Mr Séamus McKenna (49) and Mr Séamus Daly (33).
Mr Victor Barker, whose 12- year-old son James was among those killed in Omagh, said last night Mr Adams and Mr McGuinness must testify.
"This is a crucial part of the case," he said. "We want to establish how the 'Real IRA' came into existence and their evidence is vital."