Requests for more information about the Kingsmill massacre have fallen on deaf ears in the Irish Republic, a lawyer alleged.
Relatives of 10 Protestant workmen shot dead by the IRA in South Armagh in January 1976 want details about weapons used, intelligence and the getaway van employed by the gunmen.
They accused the Garda and the Irish Government of only paying “lip service” to their concerns.
Alan Kane QC for the Kingsmill victims told a Belfast preliminary hearing: “There is a level of concern based on the failure of the southern authorities to meaningfully engage with the requests, which really have fallen on deaf ears.”
Foreign Affairs Minister Charlie Flanagan has said Dublin is in “direct contact” with the coroner conducting an inquest into the killings.
Lawyers for the coroner are due to meet representatives of Ireland’s state solicitor’s office soon.
Mr Kane said: “The system that has been established to deal with this aspect of legacy in Northern Ireland is being obstructed by the failure of the Irish Republic to do anything meaningful to assist.”
The victims were lined up on a country road in rural south Armagh and shot dead in a sectarian attack blamed on the IRA. Alan Black survived despite being shot 18 times.
Mr Kane said the soft Irish border of the last century had allowed heinous massacres like Kingsmill to take place.
He said: “That soft border which allowed that has been replaced by a hard border of failing to provide meaningful cooperation and disclosure to the inquest.”
He said the relatives felt mere lip service was being paid to their desire for full disclosure.
“The entire intelligence framework, the information concerning the suspect, information relating to weapons, issues relating to the palm print, those are just a few matters that we would certainly be wanting more information.”
The coroner’s court inquiry is due to resume in May after prosecutors decided a man would not face prosecution over a palm print found on the get away van used by the gunmen.
Around 1,000 pages of new material were created by the most recent criminal investigation, lawyer for the coroner Sean Doran QC said.
Mr Kane said most of the information disclosed so far by the Republic was newspaper cuttings.
“A librarian could do it.”
He said relatives were sceptical members of the Irish Government or Garda were taking meaningful steps.
“They feel that this is but a window-dressing exercise that is being carried out by the authorities in the Irish Republic at the very last moment, knowing full well that this inquest is scheduled to take place in two months time.”
Another lawyer characterised it as “pulling teeth” and said the official response had been “disingenuous”.
Another preliminary hearing is due next month.