The home secretary has ordered a review by a former senior judge into the role police corruption played in shielding the murderers of a private detective found with an axe embedded in his head.
Daniel Morgan was murdered in a south London pub car park in March 1987, and his killers have never been brought to justice.
His family believe he was silenced as he prepared to expose corruption at the highest ranks of the Metropolitan police.
The Home Office announced on Friday that an independent panel would examine the case, chaired by the former appeals court judge Sir Stanley Burnton.
It will be a painful exercise for Scotland Yard, which in 2011 accepted that police corruption had shielded the killers, in a letter written by the then acting commissioner, Tim Godwin.
The review is also challenging for News International, which owns the Sun, the Times and the Sunday Times. In 2002, the News of the World placed under surveillance the head of the Morgan murder investigation, the former detective chief superintendent David Cook – allegedly on the orders of an executive. The paper physically followed Cook and his young children, "blagged" his personal details from police databases, and tried to access his voicemail and that of his wife.
Cook, a former Met detective, said the inquiry could be as difficult for the Met over the issue of corruption as the public inquiry in 1998 into the Stephen Lawrence case was on the force's racial failings.
He said: "I consider the Daniel Morgan murder as grave a case for the Metropolitan Police as was the murder of Stephen Lawrence, but instead of race being the issue, this time it is about corruption."
The announcement of the inquiry is a victory for the Morgan family, who have battled powerful institutions for over a quarter of a century. Morgan's brother Alastair said the fight they had been forced to wage amounted to "mental torture" and criticised police chiefs over the years who he said had failed to tackle corruption so serious that it had shielded murderers.The review announced on Friday is the second ordered by the home secretary into allegations that past Met corruption shielded murderers. One is already under way into allegations that officers helped protect the killers of Stephen Lawrence, and is being conducted by a senior prosecutor.
Theresa May said the panel would "shine a light" on the circumstances of Daniel Morgan's murder, its background and the handling of the case since 1987.
Alastair Morgan, Daniel's brother, said: "Through almost three decades of public protests, meetings with police officers at the highest ranks, lobbying of politicians and pleas to the media, we have found ourselves lied to, fobbed off, bullied, degraded and let down time and time again. What we have been required to endure has been nothing less than mental torture.
"The allegations and evidence of serious corruption within the Metropolitan police – extending to recent history and the highest ranks – remained unaddressed through five police investigations."
He added: "Over most of this period, we witnessed a complete unwillingness by police and successive governments to face up to what was occurring, and ultimately a complete failure by police leadership to deal effectively with serious police criminality."
The Morgan family said the terms of reference for the inquiry panel included:
Police involvement in the murder
The role played by police corruption in protecting those responsible for the murder from being brought to justice and the failure to confront that corruption
The incidence of connections between private investigators, police officers and journalists at the News of the World and other parts of the media and corruption involved in the linkages between them.
In 2011, the trial of three men accused of Morgan's murder collapsed over legal technicalities and police errors.
The prosecution decided not to offer any evidence because it could not guarantee the police could meet rules protecting the defendants' right to a fair trial. Charges against two other men had been dropped earlier.
One of those acquitted was a former detective, Sid Fillery, who was charged with perverting the course of justice. After the murder he replaced Morgan at Southern Investigations.
The brothers Garry and Glenn Vian were also acquitted, after the prosecutor had to admit police could not be relied upon to ensure the defence had access to any documents detectives may have which could be relevant to resisting the charges.
The case is estimated to have cost between £30m to £50m in investigations and trials over the 26 years since the murder.