The survivors of the Miami Showband massacre have urged former soldiers who suspected that their ranks had been infiltrated by loyalists to help shed light on the UVF atrocity.
Three members of the popular cabaret band were shot dead by a UVF gang after being flagged down as they drove back to Dublin following a gig in Banbridge, Co Down in July 1975.
Lead singer Fran O'Toole (29), guitarist Tony Geraghty (23) and trumpet player Brian McCoy (33) were killed in a hail of bullets.
The killer gang opened fire after two of its members had blown themselves up as they attempted to plant a bomb inside the band's bus.
The gang included a number of rogue Ulster Defence Regiment (UDR) soldiers. It had flagged down the bus after setting up a fake UDR checkpoint on the A1 in Co Down.
The two band members who survived the massacre - Des Lee and Stephen Travers - are currently taking legal action against the police and Britain's Ministry of Defence.
Their claim, which also involves the widows of Mr O'Toole and Mr McCoy, focuses on the contention that the UDR did not do enough to prevent collusion with loyalists at the time.
Days after the 40th anniversary of the attack, they have appealed for former UDR soldiers to help their quest for justice.
Michael Flanigan, the Belfast solicitor representing the survivors and bereaved families, said: "It is well established that by the time the attack took place, the UDR had experienced years of infiltration by, and regular loss of weapons to, loyalist paramilitaries.
"We would like to hear from former UDR members who may have reported concerns about collusion to their superiors within the regiment."
Mr Flanigan urged anyone with information to contact his office on 02890 233309 or email firstname.lastname@example.org.