An investigation has been launched by the Independent Police Complaints Commission (IPCC) into how files from the Lynette White investigation came to be destroyed.
The destruction of the files on the orders of cold-case investigator Detective Chief Superintendent Chris Coutts, a court heard, led to the collapse of a corruption case against eight former police officers.
South Wales Police referred the matter to the IPCC after the collapse of the trial, in which 10 people were accused of fabricating a case that led to the wrongful conviction and imprisonment of three men for the murder of Miss White.
A spokesman for the IPCC said its inquiry "will look at issues surrounding the destruction of copies of files by South Wales Police officers".
The body of the 20-year-old prostitute was found at her flat in Cardiff in 1988. She had suffered more than 50 stab wounds.
Stephen Miller, Yusef Abdullahi and Tony Paris were charged and convicted of murder and they spent two years in prison before being released on appeal. In 2003, Jeffrey Gafoor, a client of Miss White's, admitted her murder and is now serving a life sentence.
Following Gafoor's arrest, an investigation was carried out into the original convictions. Ten people were accused of bullying witnesses into making up accounts of the killing. They faces charges of conspiracy to pervert the course of justice or perjury.
The file that Mr Coutts, who headed the cold-case review, had given the order to destroy was a copy of material relating to a complaint made by John Actie to the IPCC. Keir Starmer, QC, the Director of Public Prosecutions, spoke of his "extreme concern".