The true reason for the brutal murder of Daniel Morgan in 1987 may never be known, but several motives have been considered over the decades.
A report by an independent panel published on Tuesday detailed several possible theories as to why the private investigator was killed.
Central to many of the theories was the idea of involvement of corrupt police officers who felt Mr Morgan may reveal their crimes.
The report accused the Metropolitan Police of “a form of institutional corruption” for concealing or denying failings over Mr Morgan's unsolved murder.
The Metropolitan Police accepted this and said they "deeply regret" their failure to bring Mr Morgan's killer to justice and accepted "corruption and the malicious acts of corrupt individuals were a major factor in the failure of the first investigation."
Met Commissioner Dame Cressida Dick also apologised and said it is a “matter of great regret that no one has been brought to justice and that our mistakes have compounded the pain suffered by Daniel’s family”.
Metropolitan Police Assistant Commissioner Nick Ephgrave apologises for the failures and says the Met "seeks to do the best it can" in his experience
Was Daniel Morgan about to reveal links between corrupt officers and organised crime?
One of the theories behind Mr Morgan's death was that he was on the verge of revealing links between corrupt police officers and organised criminals.
In February 1987, he recovered a 4×4 vehicle from Malta that was connected to an ongoing fraud investigation in Yorkshire.
The report said: “Individuals linked with organised crime and allegedly to corrupt police officers were associated with a Range Rover recovered from Malta by Daniel Morgan in February 1987.
“West Yorkshire Police were investigating individuals suspected of committing major fraud and one of those individuals had removed the Range Rover which had been recovered by Daniel Morgan.
“That individual was on bail in London at that time.”
Mr Morgan had also mentioned to friends that he had information that he could sell to a Sunday paper for £250,000.
Business associate Bryan Madagan said that in May 1987, Mr Morgan had told him that he had been offered the money by a newspaper for an expose on how he got information.
Was Daniel Morgan's murder linked to the death of a police officer?
Another theory was that the murder could have been linked to the death of police officer DC Alan Holmes, known as Taffy, who took his own life in July 1987.
It was suggested by Mr Morgan's former business partner Jonathan Rees and a former police officer called Derek Haslam that Mr Morgan and Mr Holmes wanted to sell information regarding corruption.
The panel found no evidence to back this theory.
Were police officers selling information?
Another possibility was the idea that police officers in south-east London were making money illegally selling information and moonlighting, for example as security guards, and felt that Mr Morgan threatened both the profits and their future careers.
The report said: “It is also possible that local officers involved in identified lucrative corrupt practices, such as selling confidential information, assisting criminals with inside police information and ‘moonlighting’, thought that their police careers and pensions were under threat, and that future, potentially lucrative options might be put at risk by Daniel Morgan’s alleged intention to reveal what he knew.
“The evidence supporting this theory as to why Daniel Morgan was murdered was never seriously investigated, despite the fact that in the years following Daniel Morgan’s murder, several of the police officers connected to Daniel Morgan’s circles and business were investigated for and convicted of serious crime.”
Daniel Morgan's work as a bailiff
Mr Morgan had also worked as a bailiff and repossessing cars, and the day before his murder had served a court summons on a man who had previous convictions for violent offences.
Other possible motives considered were Mr Morgan trying to identify a drug dealer who was selling illegal substances to a client’s daughter; a possible killing by the jealous husband of one of the women Mr Morgan allegedly had an affair with; and a dispute over the theft of a stereo from his car and threats made by the youths who had taken it.