The High Court in Belfast will rule today on an application for an FBI agent to give satellite evidence in a landmark civil action brought by relatives of people killed in the Omagh bomb.
Families of some of the 29 people killed in the August 1998 atrocity would like David Rupert, who infiltrated the Real IRA, to testify in a civil action against five people.
Former Real IRA chief of staff, Michael McKevitt, who was jailed in August 2003 for 20 years at the Special Criminal Court in Dublin for directing terrorism, is among those being sued by the families.
The action is also being taken against Colm Murphy, who received a 14 year prison sentence from the Special Criminal Court in Dublin in January 2002 for conspiring to cause an explosion.
The other people named in the civil action are Seamus McKenna from Silverbridge in Co Armagh, Liam Campbell from Dundalk and Seamus Daly from Castleblaney, Co Monaghan who in March received a three and a half year jail sentence from the Special Criminal Court for Real IRA membership.
In June of last year, the High Court was told Mr Rupert, a key witness in the action, was living in fear for his life. The agent is believed to have been living under a witness protection scheme in the United States.
Lawyers acting for the families believe Mr Rupert's life could be put at risk if he is asked to travel to Belfast to testify in court. In June 2003, the agent gave evidence against McKevitt during his trial in Dublin.