Alleged security force collusion in the loyalist murders of eight men in South Armagh in the 1970s was not properly investigated, the ECHR has ruled.
The cases covered include eight murders and a wounding
The cases were taken to the European Court of Human Rights after a collusion claim was made by a former RUC officer, John Weir, on a television programme.
He said a farmhouse owned by another police officer was used as a base from which to carry out a series of murders.
The cases include the Reavey brothers' murder at Whitecross in January 1976.
The unanimous judgement also covered the murders of Joseph, Barry and Declan O'Dowd, who were killed on the same evening as the Reavey brothers (John, Brian and Anthony).
John Weir is a former RUC sergeant who was convicted for the murder of Catholic shopkeeper William Strathearn in April 1977.
Eight years ago, he claimed to have been a member of the loyalist gang which carried out these and other murders. He said the gang consisted of members of the RUC, UDR and the UVF.
The RUC launched an investigation, but did not interview Weir, who now lives in Africa, as he was said not to be a credible witness.
The European Court of Human Rights awarded all applicants 5,000 euro in respect of non-pecuniary damage and 5,000 euro in respect of costs and expenses - with the exception of the family of Trevor Brecknell where the award was 51,000 euro.
Mr Brecknell was murdered at Donnelly's Bar in Silverbridge in December 1975.
Other cases covered by the ruling were the murder of Colm McCartney at Altnamackin in August 1975 and the wounding of Michael McGrath in a gun attack on the Rock Bar in Keady in June 1976.
Fearghal Shiels of Madden & Finucane solicitors said: "In 1999 the RUC purported to conduct a police investigation into John Weir's allegations.
"The RUC took no steps to interview John Weir and irrespective of the cogent and credible evidence of widespread collusion by members of the UDR and RUC with a loyalist murder gang based in Mid-Ulster, concluded that his allegations were false."
A collusion claim was made by former RUC officer John Weir
"Today's findings by the European Court of Human Rights that the families' human rights were breached by the UK Government vindicates the families' central contention that there was a total lack of independence, transparency and accountability on the part of the RUC, in investigating the activities of this murder gang."
The families are now said to be discussing with their solicitors the implications of the ruling.
Sinn Fein Newry and Armagh MP Conor Murphy welcomed the ruling.
"This unanimous ruling today highlights the lack of independence within the RUC investigation into the allegations of collusion, but there are many other unanswered questions about the relationship between this loyalist gang and members of the RUC and UDR," he said.