Trevor Birney and Alex Gibney attend the 55th New York Film Festival - 'No Stone Unturned' at The Film Society of Lincoln Center, Walter Reade Theatre on September 30, 2017 in New York City. Paul Zimmerman/Getty

Producer Trevor Birney and journalist Barry McCaffrey, who worked on “No Stone Unturned” with Academy Award winner Alex Gibney which investigated the massacre of six innocent football fans in a Co Down pub, have been freed on bail.

Speaking to the media outside the police station McCaffrey. stated their arrest was an attempt to silence the media.

The film, released last November, examined issues surrounding the murders of six men who died in the small village of Loughinisland as they watched a World Cup soccer game on television in June 1994.

The documentary named who they thought was responsible, including the lead gunman who still lives in the area. It is believed their arrests are connected to that issue.

Birney is widely regarded as the best investigative journalist in Ireland. He was a co-producer on the Oscar-shortlisted, Alex Gibney feature-documentary, “Mea Maxima Culpa: Silence in the House of God,” for which he received an IFTA, an Irish Oscar, in February 2013.

Read more: Chief suspects in Loughinisland massacre named for first time in new documentary

He has also won a Justice Media Award, two Royal Television Society awards, has been nominated for three others and was named NI Broadcaster of the Year in 2002.

It has been reported that the arrests are in connection with the alleged theft of confidential documents from the Police Ombudsman of Northern Ireland in relation to the killings.

The massacre caused outrage all around Ireland and cast a huge shadow over the celebrations after the Irish team shocked the Italians with a 1-0 win, in a game which was likened to a home game for the Republic as there were so many Irish fans in the Giant’s Stadium at the time.

A 2016 report from the Ombudsman found that there had been collusion between the Royal Ulster Constabulary (RUC) and the UVF killers, and it also found that the police investigation had been undermined by a desire to protect those responsible for the six murders.

Read more: New documentary names alleged Loughinisland mass killer

The Ombudsman’s findings were subsequently challenged in court, but Gibney’s film reopened the controversy over collusion last year when it explored the unsolved killings in detail and even named the three chief suspects in the murders for the first time.

Following the release of “No Stone Unturned,” bereaved family members called for arrests, prosecutions, and accountability, as nobody has ever been charged in relation to the atrocity.

The six innocent men - Adrian Rogan (aged 34), Patrick O’Hare (35), Eamon Byrne (39), Malcolm Jenkinson (53) Daniel McCreanor (59) and Barney Greene (87) - were in the Heights Bar when two gunmen from the Ulster Volunteer Force (UVF) burst in and sprayed the premises with bullets.

Read more: A survivor’s tale: The 1994 Loughinisland massacre

The men were watching a game between the Republic of Ireland and Italy from the Giant’s Stadium, New York, at the time of the massacre. The film claimed that RUC officers were aware of the UVF plans to kill; that evidence, including the killers’ getaway car, had been destroyed; and that suspects were given advance warnings that they were about to be interviewed about the killings.

“No Stone Unturned,” which features an interview with IrishCentral founder Niall O’Dowd, reawakened interest in the massacre – and the families’ desire for accountability – upon its release last November.

On Friday, director Alex Gibney confirmed the arrests of his two colleagues on social media. He described them as “outrageous” on Twitter.

A spokesperson for Five Point Films confirmed to the BBC that the two men, aged 51 and 48, were arrested on Friday morning and declined to make further comment “until the process is concluded.”

Both investigative journalists played key roles in researching collusion between the police and the loyalist killers for Gibney’s documentary film.

Search warrants were executed at three properties in the Belfast area on Friday, documents and computer equipment were seized, and the two men were being held at Musgrave Police Station on Friday afternoon.

Amnesty International has expressed deep concern at the arrests of Birney and McCaffrey in Belfast.

“The arrests of two widely respected investigative journalists and the seizure of documents and computer equipment is of deep concern to Amnesty International,” said Northern Ireland Programme Director Patrick Corrigan.

“Journalists must be free to investigate and expose issues of public concern. Few subjects could be of more significant public concern than the mass shooting of civilians and the alleged collusion of the police in assisting those responsible to evade justice.

“These arrests will send a worrying message to other journalists in Northern Ireland and could have a chilling effect on legitimate investigative reporting.”

The alleged theft of documents from the Police Service of Northern Ireland (PSNI), which has replaced the disbanded RUC, led the PSNI to call in the Durham Constabulary form the United Kingdom to carry out an independent investigation.

Detectives from Durham, supported by officers from the PSNI, carried out the search warrants at the three Belfast properties and it is understood the two men were arrested in relation to sensitive material which was used in Gibney’s documentary movie.

The National Union of Journalists in Ireland and Britain have expressed “grave concern” at this morning's arrests in Belfast, which they have described as deeply worrying.

Journalists are particularly concerned by the confiscation of computers and data relating to the investigation into the killings.

"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," said acting general secretary Seamus Dooley.

"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. These journalists are entitled to claim journalistic privilege and to seek the protection of the legal system  if there is any attempt to force them to reveal sources."

Mr. Dooley said the investigative reporters had a right to lawfully protect confidential sources. 

"Journalists throughout the UK and Ireland will support Trevor and Barry in any stand they take," he said. "It is profoundly depressing to note that, yet again, priority appears to be given to tracking down the source of journalistic stories rather than solving murders in Northern Ireland.”

Ciaran Tierney is a journalist, blogger, and digital storyteller, based in Galway, Ireland. Find him on Facebook here.