The British Prime Minister's refusal to hold a public inquiry into the murder of Belfast solicitor Pat Finucane was morally and legally indefensible, a court has been told.
A barrister representing Mr Finucane's wife Geraldine alleged that David Cameron rejected an inquiry into claims of state collusion with the loyalist paramilitary killers over fears of criticism from elements of the Conservative Party and the right-wing press in the UK.
Pat Finucane's brother Seamus, daughter Katherine and son John at the High Court in Belfast today.
Belfast High Court is hearing a judicial review by Mrs Finucane of the decision by Mr Cameron to rule out an inquiry into the 1989 Ulster Defence Association (UDA) shooting in the city.
Opening the case before judge Mr Justice Stephens, Barry MacDonald QC said the murder was one of the "most notorious" of the Troubles.
"It is notorious for good reason," he added. "The available evidence suggests that agents of the state responsible for law enforcement devised and operated a policy of extra-judicial execution, the essential feature of which was that loyalist terrorist organisations were infiltrated, resourced and manipulated in order to murder individuals identified by the state and their agents as suitable for assassination.
"In other words 'murder by proxy' whereby the state itself engaged in terrorism through the agency of loyalist paramilitaries."
The barrister added: "The decision not to hold one (an inquiry) is indefensible both morally and legally."
The solicitor's family has long campaigned for a full independent public inquiry into the murder, but Mr Cameron has insisted such an exercise would not shed any more light on the events.
A UK government-commissioned review of the controversial murder published by Desmond de Silva detailed shocking levels of state involvement.
That included spreading malicious propaganda that Mr Finucane was sympathetic to the IRA; one or possibly more police officers proposing him as a target to loyalists; and the mishandling of state agents inside the UDA who were involved in the murder.
While de Silva found no evidence of an overarching conspiracy by the authorities to target the 38-year-old lawyer, he said the actions of a number of state employees had "furthered and facilitated'' the UDA shooting, while there had also been efforts to thwart the subsequent criminal investigation.
As he accepted the report's findings in the House of Commons in December 2012, Mr Cameron reiterated an apology to the Finucane family and also pledged that the British government would examine the review in detail to identify potential lessons.
Mr Finucane was gunned down in front of his wife Geraldine and their three children inside their north Belfast home in February 1989.
Mr MacDonald outlined details of the various collusion investigations that examined the Finucane murder in the years following the shooting.
He referred to government papers that acknowledged the police and army engaged in an "active and significant obstruction" of an investigation carried out by former Metropolitan Police deputy commissioner John Stevens.
The barrister also revealed that as well as three investigations carried out by Stevens, the British government conducted its own confidential assessment of the collusion claims in 1999 - a never-published document entitled the Langdon report.
The existence of the report emerged only during the legal discovery process ahead of the judicial review.
Mr MacDonald said all the various investigations detailed evidence that warranted examination in a public inquiry.
The barrister then focused on a commitment made by the UK government at Weston Park in 2001 during peace process negotiations with the Irish government.
The Weston Park talks resulted in Canadian judge Peter Cory being asked to examine the grounds for public inquiry in a number of controversial Troubles deaths.
The Government said such inquiries would be implemented if the judge recommended that course of action.
Judge Cory subsequently did recommend public inquiries for a number of killings, including Mr Finucane's.
But while the British government ordered inquiries into the other deaths, it has not given the green light for one in the Finucane case.
Mr MacDonald said the Government's pledge at Weston Park established a "legitimate expectation" that an inquiry would be held.
He said the change of administration in May 2010, with Mr Cameron's coalition government taking over from Labour, was soon followed by the decision to reject a public inquiry and instead commission de Silva's review of the case documents.
The barrister insisted only a public inquiry could establish the full facts behind the collusion that happened.
"It is difficult to imagine a more serious allegation against a liberal democracy founded on the rule of law," he said.
"Patrick Finucane was a victim of this policy. He was identified by state agents as suitable for assassination and duly shot dead in front of his family in a particularly brutal fashion."
Mr Finucane's son John and daughter Katherine were in court for today's hearing, as was the murdered solicitor's brother Seamus.