Relatives of victims of one of Northern Ireland's worst terrorist atrocities have won permission to seek to have a report into the bombing quashed.
Fifteen people were killed in the Ulster Volunteer Force bombing of McGurk's Bar in December 1971.
Their families are challenging a Historicial Enquiries Team (HET) review that found no evidence of bias in the original police investigation.
A high court judge has ruled they have a case that the conclusions are wrong.
He granted leave to seek a judicial review, with the case now set to move to a full hearing later this year.
Four years ago, a Police Ombudsman probe identified investigative bias in how the Royal Ulster Constabulary (RUC) handled the case.
It concluded that police failed to properly investigate loyalist responsibility for the north Belfast bombing because they were focused on the idea that the IRA was to blame.
But the HET later reached a different conclusion, claiming no evidence of any bias on the part of the RUC investigators.
Those findings are being challenged in proceedings brought by Brigid Irvine, whose mother Kathleen was among the victims.
In court today her barrister detailed new material provided to HET investigators by the victims' families.
He argued that the HET findings were irrational and contrary to the overwhelming weight of evidence
He asked: "How, with all this body of information, the conclusion could be reached rationally that there was no investigative bias at play on the part of the RUC?
"In our submission, it's a question which beggars belief."
A second ground of challenge was based on an alleged failure to carry out an investigation that complied with Article 2 of the European Convention on Human Rights.
The court was told the HET findings represented a "gloves off" attack on the ombudsman's conclusions.
A lawyer for the Police Service of Northern Ireland's chief constable said the HET probe did not "besmirch or belittle" the outcome of the ombudsman's inquiries.
The judge said leave to seek a judicial review was being granted on both grounds of challenge.
Afterwards, Ms Irvine's solicitor said the families were "being re-traumatised every time they have to go to court".
But he added that they welcomed the chance for the court to "examine the way in which the HET conducted its investigation".