An investigation has been launched into the destruction of files which led to the collapse of the Lynette White police corruption trial.
The police watchdog will probe allegations against South Wales Constabulary after the multimillion-pound court case was dramatically thrown out on Thursday.
Eight former police officers walked free after hearing that top cold case officer Detective Chief Superintendent Chris Coutts had ordered the destruction of evidence.
A spokesman for the Independent Police Complaints Commission said its inquiry "will look at issues surrounding the destruction of copies of files by South Wales Police officers which contributed to the premature end".
The police watchdog said the South Wales force had voluntarily referred the matter to investigators.
Ten people in total were on trial accused of fabricating a case which led to the wrongful jailing for murder of three men. They were formally found not guilty after judge Mr Justice Sweeney discharged a Swansea Crown Court jury, telling them the accused could not get a fair trial.
South Wales Police Chief Constable Peter Vaughan backed calls for a "full and detailed review" of the circumstances in which the decision to end the trial was made.
The investigation came in the wake of the brutal murder of prostitute Miss White in a seedy flat in Cardiff in 1988. The 20-year-old was found with more than 50 stab wounds in her body.
Police eventually arrested Stephen Miller, Yusef Abdullahi, Tony Paris and cousins Ronnie and John Actie for murder. The cousins were cleared but the three other men went on to serve two years in prison before being released on appeal.
In 2003, Jeffrey Gafoor, a client of Miss White, pleaded guilty to her murder and is now serving a life sentence.
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