The force watchdog today published the findings of its lengthy inquiry into the scandal, which saw the murder convictions of five men quashed over the amateur footballer's slaying, saying they failed in their 'professional, ethical and moral obligation'.
The 587-page 'Operation Kalmia' report recommended that former Staffordshire Chief Constable Jane Sawyers, ex-Northamptonshire Chief Constable Adrian Lee, retired-Gloucestershire Chief Constable Suzette Davenport, and current West Midlands Assistant Chief Constable Marcus Beale face multiple counts of alleged gross misconduct.
All were Staffordshire police officers at the time of the Nunes fiasco.
Ultimately, none faced any disciplinary action after the findings were overruled by their respective police and crime commissioners and former West Midlands Chief Constable Chris Sims.
WATCH Express & Star investigations editor Rob Golledge analyses the botched investigation
The inquiry centred around whether a damning internal police management review, which looked into wrongdoing by detectives and the handling of the case's star witness, was suppressed by officers.
The dossier was never revealed to the judge, jury or barristers at the original Nunes murder case.
Had it been it would have cast serious doubt on the integrity of the police's case.
The Operation Kalmia report, compiled by then-Derbyshire Chief Constable Mick Creedon, found there was no evidence of corruption but that the officers failed in their duty.
The report, which is redacted in several places, was published alongside a 47-page summary by the Independent Police Complaints Commission.
The IPCC now says its position is that no disciplinary proceedings should take place – even though it is at odds with its investigator's report.
The summary states: "Whilst the IPCC has accepted that there should be no disciplinary proceedings for the senior officers, it remains concerned that there were clearly significant failures by Staffordshire Police that ultimately resulted in the unsafe convictions of five individuals for murder. This is extremely serious and it is critical that such failures are avoided in future."
It added: "The investigator found no evidence of a deliberate decision to conceal the management review, however there was a failure to ensure that it was disclosed as it should have been.
"The investigator found that whilst it was not possible to show that the officers were under a specific duty under the Criminal Investigations and Procedures Act 1996 (CIPA) or common law to ensure that it was disclosed, there was a personal, professional, ethical and moral obligation placed on all police officers to ensure that facts relevant to an impending court case, a trial or even to an existing conviction are properly considered and where appropriate are brought to the attention of the court.”
All the senior officers deny any wrongdoing, and some have criticised the IPCC's report.
A total of 14 Staffordshire officers were placed under investigation by the watchdog.
Chief Constable, Gareth Morgan, said: "Since becoming Chief Constable, I have read in detail the Independent Police Complaints Commission (IPCC) report outlining their findings into Staffordshire Police’s investigation of the murder of Kevin Nunes in 2002. I have also had the opportunity to review associated reports and correspondence relating to Staffordshire Police.
"It is clear that following a lengthy process, both the CPS and IPCC found no evidence of corruption or criminality in the actions of Staffordshire Police. However, significant police failures were highlighted, for which, on behalf of the Force, I apologise.
"I am particularly sorry that the family of Kevin Nunes have not received justice for his death, and for the length of time it has taken these matters to reach a conclusion. I know they have been let down.
"In 2005, there were failings in the management of protected witnesses and in the disclosure of relevant material to the Crown Prosecution Service and the courts.
"Since the initial investigation things have changed. Numerous processes have been put into place to ensure all information is recorded appropriately, retained, and the necessary disclosure takes place. This follows national guidance and protocol.
"I am clear that the integrity of all our investigations must remain high, to protect the judicial outcome. As a result of the robust processes we have put in place, I am confident that this would not happen again.
"The investigation into Kevin’s murder remains open. As with all our unsolved crimes in Staffordshire these are subject to regular reviews to identify new potential lines of enquiry.
"This has been a complex and protracted matter that has also been the subject of civil claims which have now settled.
"It is now time for us to acknowledge our mistakes, to learn and to move forwards to deliver the very best service we can to the communities of Staffordshire and Stoke-on-Trent."
More background to the investigation
Kevin Nunes, of Whitmore Reans, Wolverhampton, was shot in a 'gangland execution' in Pattingham, Staffordshire, in September 2002.
In 2008, five Black Country gangsters Adam Joof of Willenhall, Levi Walker of Birmingham, Antonio Christie of Great Bridge, and Owen Crooks and Michael Osbourne both of Wolverhampton were given life sentences after being found guilty of the 20-year-old's murder at Leicester Crown Court.
But four years later the five men had their convictions quashed in the Court of Appeal.
The court revealed serious police failings and concerns had not been disclosed at the original murder trial.
It exposed that detectives drunk alcohol with the star witness, covered-up alleged crimes committed by the witness, and allegedly abused overtime to boost their pay
One of the witness handlers was having an ‘intimate affair’ with the female officer in charge of overseeing evidence.
And it revealed the unit was dysfunctional, detectives didn’t trust each other, and unveiled major concerns over the integrity of the officers.
The scandal was exposed by ex-Detective Inspector Joe Anderson who turned whistleblower in the case.
This year Walker and Christie were paid £200,000 in damages by Staffordshire Police.