Gardaí and the Taoiseach have been criticised for reneging on their pledge to hand over files on the Kingsmill massacre.
The criticism comes after Taoiseach Enda Kenny two months ago committed publicly to handing over the files.
Lawyer Fiona Doherty QC, who represents the sole survivor of the attack on Alan Black, was scathing after authorities said they were not in a position to give a date for disclosure.
She said Mr Kenny's pledge had raised "considerable expectation" among the families.
The murders, which were widely blamed on the IRA though the organisation never admitted responsibility, involved a cross-border element, with the vehicle used by the killers both stolen and then dumped in Co Louth.
Mr Kenny's remarks seemed to end months of uncertainty over whether the new inquest would be able to access the potentially crucial Garda papers.
In a statement this evening the Government said: "The Irish Authorities remain committed to the provision of information to the Northern Ireland Coroner in the context of the Kingsmill Inquest.
"The authorities here remain in ongoing contact with the Northern Ireland Coroner's Office and are anxious to ensure that records can be provided as soon as is possible in accordance with the law", it added.
Barrister Neil Rafferty, acting for Beatrice Worton whose son Kenneth was killed, told coroner John Leckey that without the Garda files the inquest could only investigate "half of the story".
"My clients and other families met An Taoiseach in March and face-to-face, eye-to-eye were told this material would be looked at, it would receive full co-operation and it would be with your office within two weeks," he said.
"Quite simply my elderly clients can't reconcile what someone like An Taoiseach says and the correspondence that your officials have received from the solicitors in Dublin.
"We can't reconcile that at the highest political level we are told this will receive full co-operation yet when it gets to the official solicitor's offices not one paper clip, not one sheet of paper, has made its way north."
Mr Rafferty said his clients did not blame Mr Kenny.
"There is the political will at the highest level to co-operate," he said. "But at a lower level there seems to be an inexplicable delay in co-operating."
Mr Leckey, who in March welcomed Mr Kenny's statement, said the Taoiseach would not have made such comments lightly.
"When the Taoiseach said what he said it wouldn't have been off the cuff remarks, they would have been considered," he said.
The latest letter from the lawyers in Dublin who are handling the disclosure said "outstanding issues" still had to be resolved before a date for handover could be fixed.
Mr Leckey told his legal representatives to request that the state solicitor's office provide a firm timetable by the end of the month.
He said if none was forthcoming, he would consider raising the issue with Northern Ireland Secretary Theresa Villiers in a bid to resolve it with dialogue between the two governments.
The protestant textile workers were gunned down after a masked gang stopped their minibus close to the Co Armagh village of Kingsmill as they were travelling home from work.
They were forced to line up alongside the van and ordered to divulge their religion.
The only Catholic worker was told to flee the scene while the 11 remaining workers were shot.
Mr Black, who survived despite being hit 18 times, was in court today.
No-one has ever been convicted of the murders.
