Updated 21:30

Two journalists arrested over the suspected theft of confidential documents related to the Loughinisland murders have been released by police in Northern Ireland.

Trevor Birney and Barry McCaffrey were arrested in Belfast this morning.

Both men worked on a documentary raising serious questions about the police investigation into the 1994 loyalist terror attack in County Down.

This afternoon, the National Union of Journalists in the UK and Ireland expressed its “grave concern” at the arrests.

Meanwhile, families of those killed in the massacre staged a vigil in solidarity with the journalists.

Police said the arrests were in connection with the alleged theft of documents related to a probe by the Police Ombudsman of Northern Ireland (PONI) into how the original police investigation into the massacre was carried out.

The material is said to have been used in the ‘No Stone Unturned’ documentary that re-examined the murders.

Six men were killed and five other people injured when UVF gunmen opened fire at the Heights Bar in the small County Down village of Loughinisland in June 1994.

The shooting happened while customers were watching the Ireland v Italy match during that year's World Cup.

"Deeply worrying"

This afternoon, Seamus Dooley, acting general secretary of the National Union of Journalists in the UK & Ireland (NUJ), said the documents were used in the “highly significant documentary ‘No Stone Unturned’ which deals with the murders.”

“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,” he said.

“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.”

Journalistic sources

He said police had confiscated computers and data held by the two men and warned that “every step must be taken to ensure that data held on computers is not compromised and that the confidentiality of the sources is not put in jeopardy.”

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.”

Documents

The arrests were made on foot of an investigation led by police from Durham in north east England.

Two Belfast homes and a business premises were searched by officers from the PSNI along with detectives from Durham this morning.

The two men were arrested on suspicion of theft following the searches and are being questioned at Musgrave Police Station.

Police said a “number of documents and computer equipment seized during the raids will be examined by specialist officers over the coming days.”

A police spokesperson said: "This morning’s arrests are a significant development in what has been a complex investigation.

"The theft of these documents potentially puts lives at risk and we will follow the evidence wherever it leads us."

Nobody has ever been charged in relation to the Loughinisland massacre.

A probe by the Northern Irish Police Ombudsman found the initial police investigation into the shooting was characterised by "too many instances by incompetence, indifference and neglect."

The journalists were released by police this evening.

With reporting from Michael Staines ...