Victims of the Miami Showband massacre are suing the British Ministry of Defence and the PSNI over alleged collusion with the loyalists who carried out the killings.
Three members of the band, Fran O'Toole, Tony Geraghty and Brian McCoy, were shot dead after performing in Banbridge in Co Down in July 1975.
Two other band members, Des McAlea and Stephen Travers, were wounded in the shooting but survived the atrocity.
The legal action is being taken by Mr McAlea, Mr Travers and the families of Mr O'Toole and Mr McCoy.
The case is expected to be heard next year in the High Court in Belfast.