Staffordshire Police says publishing the report would 'undermine the human rights' of the officers or any person involved and mentioned in the document.
The Express & Star requested a copy of the 73-page Costello Report into the conduct of Staffordshire Police's Sensitive Policing Unit under the Freedom of Information Act.
The contents of the report, completed in February 2007, was never disclosed by police at the original trial of five men charged with Mr Nunes' murder later that year.
But four years after the men were found guilty and jailed for life, the Court of Appeal quashed the convictions after the report came to light.
The Court of Appeal heard that the document contained details of detectives going to nightclubs and drinking alcohol with the prosecution's star witness Simeon Taylor.
But it has never been made fully public. Mr Nunes was a promising amateur footballer with Stafford Rangers and had been on the books of Tottenham Hotspur.
The 20-year-old, from Whitmore Reans, was pistol-whipped and shot dead in a country lane in Pattingham in 2002.
South Staffordshire MP Gavin Williamson said today: "It is in the public interest and, one would have thought, the police's interest to reveal what happened once and for all.
"There is nothing to be gained by holding back this report. This was a sorry affair in which a young man lost his life and there was no justice because of police failings. It is time for the truth of what happened once and for all."
In rejecting the Express & Star's request, Staffordshire Police bizarrely said the IPCC's investigation was 'currently ongoing' despite the watchdog stating on its own website the investigation was 'complete' in November 2014.
The rejection letter added: "Any release of information that relates to an on-going investigation could prejudice and undermine that investigation. The prevention and detection of such matters could therefore be hindered.
"It would also undermine the human rights of any person involved/mentioned within the report."