The level of state collusion uncovered by a report into the murder of Belfast solicitor Pat Finucane is "shocking", Prime Minister David Cameron has said.
However, the report concluded there had been "no overarching state conspiracy".
Sir Desmond de Silva's review confirmed that agents of the state were involved in the 1989 killing and that it should have been prevented.
Mr Finucane's widow, Geraldine, has dismissed the report as a "sham" and a "whitewash".
Mr Finucane was shot dead by loyalists in front of his wife and children at his north Belfast home.
The review, published on Wednesday, found RUC officers proposed Mr Finucane, 39, be killed, said they passed information to his killers and failed to stop the attack and then obstructed the murder investigation.
It also found that an Army intelligence unit, the FRU, "bears a degree" of responsibility because one of their agents, Brian Nelson, was involved in selecting targets.
The chief constable of the Police Service of Northern Ireland, Matt Baggott, said the police fully accepted the findings of the report.
He offered a "complete, absolute and unconditional" apology to the Finucane family, saying they had been "abjectly failed".
He said that in the coming days the PSNI would discuss the report with the Police Ombudsman and the Public Prosecution Service.
"Pat Finucane's murder should never have happened and it is a catalogue of failing which now needs to be assessed to see whether there are people who can be held accountable," he said.
Mrs Finucane said the government had "engineered a suppression of the truth" behind her husband's murder.
His family have led a high-profile campaign for a full public inquiry into the murder but Mr Cameron has ruled that out.
Mrs Finucane said: "At every turn, it is clear that this report has done exactly what was required - to give the benefit of the doubt to the state, its cabinet and ministers, to the Army, the intelligence services, to itself.
"At every turn, dead witnesses have been blamed, and defunct agencies found wanting. Serving personnel and active state departments appear to have been excused.
"The dirt has been swept under the carpet without any serious attempt to lift the lid on what really happened to Pat and so many others."
The Finucanes did not co-operate with the review and the solicitor's widow said the de Silva report did not tell her much more than she previously knew about the case.
Her son, Michael, claimed the government had refused their demand for a full inquiry because it did not want people to be questioned in public.
The report concluded that Nelson did not provide his handlers with details of the plot against Mr Finucane.
It found that MI5 received intelligence two months before the killing that Mr Finucane was under threat but that no steps were taken to protect him.
It also found that MI5 helped spread propaganda against Mr Finucane in the years before he was killed.
Sir Desmond found that "in 1985 the security service assessed that 85% of the UDA's 'intelligence' originated from sources within the security forces".
And he was "satisfied that this proportion would have remained largely unchanged" by the time of Mr Finucane's murder."
Sir Desmond de Silva QC carried out the review at the government's request. The Finucanes want a public inquiry as they feared the full truth would not emerge.
In his report Sir Desmond said: "A series of positive actions by employees of the state actively furthered and facilitated his murder and that, in the aftermath of the murder, there was a relentless attempt to defeat the ends of justice.
"My review of the evidence relating to Patrick Finucane's case has left me in no doubt that agents of the state were involved in carrying out serious violations of human rights up to and including murder.
"However, despite the different strands of involvement by elements of the state, I am satisfied that they were not linked to an over-arching state conspiracy to murder Patrick Finucane."
Speaking in the House of Commons on Wednesday, Mr Cameron was strongly critical of the RUC and Army for their conduct in relation to the killing.
He said Sir Desmond concluded that there was "no political conspiracy" over the murder but that "ministers were misled".
Mr Cameron added that the report found "no evidence whatsoever that any government minister had fore-knowledge of Mr Finucane's murder".
He said that on behalf of the government and the whole country he wanted to say to the Finucane family that he was "deeply sorry".
Last year, Mr Cameron acknowledged there was state collusion in Mr Finucane's murder and apologised to his family.
In the report, Sir Desmond found that an account one of the murderers, Ken Barrett, gave to the BBC Panorama programme about receiving intelligence from the RUC was "essentially accurate".
However, he added that some specific allegations made by Barrett against individual officers were not reliable.
Former Ulster Unionist MP Lord Maginnis of Drumglass said the apology was "ridiculous".
"The reality is that the Finucane family were an IRA family and I can illustrate that by saying that, when I gave that allegation publicly and was being sued for libel, the family retracted and paid my legal expenses," he told the House of Lords.
"So let's not fool ourselves about the godfather Finucane, who was killed."