The McCartney sisters have claimed that the man who ordered the murder of their brother oustide a Belfast bar intends to emigrate to the US to escape justice.
Robert McCartney (33) was stabbed and beaten to death by a gang of several men in January this year. Two people have been charged in connection with his murder.
Speaking in an interview with BBC's Newnightprogramme, Catherine and Paula McCartney, claimed the man responsible was "high up" in the IRA and arrangements were being made to protect him.
"The person who we believe ordered it is high up in the IRA: it's all to protect him," said Catherine.
"He's being allowed to be bigger than the whole movement," added Paula.
The five McCartney sisters and his partner Bridgeen Hagans have been forced to leave the Short Strand area of north Belfast due to what they claim is a campaign of intimidation against them.
They have been vocal critics of the IRA and Sinn Féin, travelling to Dublin, London, Europe and the US seeking justice for Mr McCartney's killers.