Northern Ireland's Police Ombudsman has faced calls to quit after a High Court judgment found he exceeded his powers by declaring that officers colluded with loyalist killers.
Unionists urged Dr Michael Maguire to consider his position after the highly critical judicial finding on his handling of an investigation into alleged officer misconduct in relation to the murder of six Catholic men in a Co Down village pub.
Last year, Dr Maguire claimed Royal Ulster Constabulary (RUC) officers colluded in the 1994 Ulster Volunteer Force sectarian massacre in Loughinisland in a landmark report that outlined a series of "catastrophic" investigative failures.
Two UVF gunmen burst into the packed bar and fired at customers watching the Republic of Ireland play Italy in the World Cup in the US.
Six were killed and five injured. Nobody has been brought to justice.
Former officers challenged Dr Maguire's findings by way of judicial review and Mr Justice McCloskey has found against the ombudsman.
He said the determination of police collision was "unsustainable in law", as it exceeded the ombudsman's statutory powers.
The judge said RUC officers involved in the case had not been been afforded the protection of due process, despite Dr Maguire's "destructive and withering condemnations" being essentially presented as a verdict on their guilt.
"They were, in effect, accused, tried and convicted without notice and in their absence," the judge said.
He added that the language and structure of sections of the report were "careless, thoughtless and inattentive".
Justice McCloskey will sit again in the new year to consider whether the ombudsman's finding should be formally quashed.
DUP MP Jeffrey Donaldson said the judgment was an indictment on Dr Maguire and said he should consider his position.
"Some of language used by the judge here is very strong and powerful language and I think that he will need to consider very carefully the implications of this and the whole question of public confidence in his office," he told the BBC.
Ulster Unionist MLA Alan Chambers said the ombudsman's position was "untenable".
"Allegations of collusion have been used to smear the reputation of the RUC and question the credibility of the justice system in Northern Ireland," he said.
"For the Police Ombudsman's Office to be the source of a report that has been so comprehensively rejected by the High Court should be a matter of huge embarrassment for the Ombudsman, and he should do the right thing and go now."
TUV leader Jim Allister said: "It is hard to think of a more damming verdict. It is time for Dr Maguire to consider his position."
Sinn Féin MLA for South Down Chris Hazzard insisted the ruling did not mean collusion did not happen.
"This is obviously a bitterly disappointing ruling but whatever criticisms have been made regarding the Ombudsman's handling of the report, that does mean that collusion was not involved in this case," he said.
"There is a wealth of evidence already established regarding the scale of state collusion with the loyalist paramilitaries who carried out the Loughinisland massacre."
The Police Ombudsman's Office expressed disappointment at the High Court judgment.
"We will need time over the coming weeks to consider it carefully," a spokesman said.
"As we look at the judgment in more detail we will examine all the options open to us including an appeal.
"Clearly, however, we have to wait until the final outcome of the challenge.
"This judgment may have implications for how Northern Ireland deals with historical matters, affecting not only this office, but also proposed solutions such as the Historical Inquiries Unit."