The murder of Mr Pat Finucane (38) by the UDA as his family gathered for Sunday lunch in February 1989 stands as one of the most notorious of the Troubles.
It was alleged after the killing that his loyalist killers were acting on implicit directions from within the security forces who claimed that the solicitor was in some way the brains behind the IRA.
Sir John Stevens, the chief of London's Metropolitan police who has been investigating collusion for the last 14 years, found that security force elements were involved in his killing.
Mr Finucane's family has accused the British government of failing to seek out the truth of this murder in particular, and all killings by loyalists with RUC and British army collaboration in general.
The Finucane family fear the British government is seeking to "delay and frustrate" the establishment of a judicial inquiry into the case and have said they believe there will be a "drip-feeding" of further prosecutions to prevent the inquiry the government agreed to establish.
Canadian Judge Peter Cory found there was a case to answer and recommended an inquiry. However, he went further and said the Finucane case was one of those rare instances where it would be worth forgetting about a prosecution in the interests of facilitating a bigger and wider inquiry.
In doing so he effectively sided with the Finucanes against the state. They believe that what matters is not the sentencing of Ken Barrett, but the revelation of the extent to which British security forces colluded with loyalist paramilitaries.
The European Court of Human Rights in Strasbourg ruled last year that the British government failed to properly investigate the loyalist murder of Belfast solictor Pat Finucane.
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.
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 was convicted and sentenced to 22 years for Mr Finucane's murder.
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".