The European Court of Human Rights in Strasbourg has ruled that the British government failed to properly investigate the loyalist murder of Belfast solictor Pat Finucane.
The seven-judge court ruled that Mr Finucane's murder was a breach of human rights.
The court backed a legal claim by Mr Finucane's wife, Geraldine, that there was no "effective" inquiry into her husband's killing and the RUC investigation lacked independence because it was conducted by officers from a force accused of making death threats against him.
Mrs Finucane also claimed the circumstances of the shooting had given rise to suspicions that the security forces co-operated with the killers in the Ulster Defence Association.
Mr Finucane (38), a Catholic lawyer, was gunned down in front of his family after gunmen burst into their north Belfast home in February l989.
Several loyalists have been at the centre of one of Northern Ireland's most controversial murders. They include:
- Brian Nelson, a UDA man who worked as an agent for British military intelligence, who first revealed the collusion claims that have been under investigation by Sir John Stevens, now Metropolitan police commissioner. Mr Nelson died of a brain haemorrhage earlier this year.
- William Stobie, another UDA double agent who was once charged with the Finucane murder after allegedly supplying the weapons. He was shot dead by former associates who feared he was planning to blow their cover.
- Ken Barrett, also an ex-UDA man arrested in England at the end of May before being brought back to Belfast to be charged with the murder. He is in custody awaiting trial.
The Stevens inquiry is expected to have a final report ready later this year, but up to 20 military and police personnel could face criminal charges.
An interim report by Sir John in April claimed: "I also believe that the RUC investigation of Pat Finucane's murder should have resulted in the early arrest of his killers.
"I conclude there was collusion in both murders and the circumstances surrounding them".