Families of a notorious massacre during the Northern Ireland troubles have condemned the arrest of two investigative journalists who worked on a documentary on the outrage.
Award winning reporters Trevor Birney and Barry McCaffrey have been detained over the suspected theft of confidential documents relating to the Loughinisland killings of 1994.
Six men were murdered when loyalists opened fire on a crowd of football fans gathered around a TV in a village pub watching the Republic of Ireland play in the World Cup.
Last year's No Stone Unturned film examined the persistent claims of state collusion in the murder and broke new ground by publicly naming what it said were suspects.
Film maker Alex Gibney, who produced the programme, described Friday's arrests as "outrageous" while the National Union of Journalists expressed "grave concern".
Relatives of the Loughinisland victims said they were "shock and appalled".
Spokeswoman for the families, Clare Rogan, said: "Today's arrests show the lengths of desperation that the British Government and state forces are prepared to go to in order to stifle the truth about what happened in Loughinisland.
"Our families and many other families across the island, some of whom have been denied the basic right to an inquest, have campaigned for many years against state collusion and for truth and justice for our loved ones.
"These actions are the latest attempt to deter the work of families and journalists who seek to shine the light on the dark levels of collusion at the heart of the British state."
The families are planning a vigil outside the bar where the attack took place on Friday evening to protest at the development.
Seamus Dooley, acting general secretary, NUJ UK & Ireland, said: "The documentary raises serious questions about the police investigation into Loughinisland and it is deeply worrying that the focus of police attention should be on journalists rather than on the issues raised in the documentary.
"The protection of journalistic sources of confidential information is of vital importance and journalists must be free to operate in the public interest without police interference."
Police said the confidential material under investigation, which officers say featured in the documentary, had been in the possession of the Police Ombudsman for Northern Ireland (PONI).
A police spokesman has claimed that the theft of the documents "potentially puts lives at risk".
PONI officers reported the theft to the Police Service of Northern Ireland. The PSNI then asked Durham Police to conduct an independent investigation into the theft.
Mr Birney, 51, and Mr McCaffrey, 48, were arrested by officers from the Durham force on Friday morning.
The arrests came on Friday morning after detectives, supported by PSNI officers, searched three properties in the Belfast area.
These included two residential properties and a business premises, understood to be a production company linked to the documentary.
A number of documents and computer equipment seized during the raids is to be examined by specialist officers.
The men are being questioned at Musgrave police station in Belfast.
A spokesman for Durham Constabulary described the investigation as "complex".
"This morning's arrests are a significant development in what has been a complex investigation," he said.
"The terms of reference given to our inquiry were clear in that the investigation is solely into the alleged theft of material from PONI.
"The theft of these documents potentially puts lives at risk and we will follow the evidence wherever it leads us."
The attack unfolded on June 18 1994 when loyalist gunmen burst into the Heights Bar and opened fire on customers.
The UVF gunmen struck as football fans watched the Republic of Ireland team play in the 1994 Fifa World Cup.
In 2011, the Police Ombudsman Al Hutchinson found there had been major failings in the police investigation following the shootings, but said there was no evidence that officers had colluded with the UVF.
However in 2016, a new Ombudsman Dr Michael Maguire found there had been collusion, and the police investigation had been undermined by a desire to protect informers.
In 2017, a judge delivered a damning judgment against Dr Maguire's report, ruling that he had exceeded his statutory powers by declaring officers guilty of colluding in the UVF attack.
Another judge is now presiding over a case that will focus on whether Dr Maguire's findings should be formally quashed.