NOBODY could accuse the old Strathclyde Police force of lacking effort in the investigation to identify who killed Emma Caldwell.

The Glasgow sex worker’s body, found in woods near Biggar in 2005, triggered one of the biggest manhunts in years. Strathclyde had a poor record in solving the murders of sex workers, but there was a marked determination in this case.

Caldwell was a former stable girl, and happy teenager, who grew up in Erskine, Renfrewshire. But in 1998, her elder sister Karen died of cancer and within a year, Caldwell had become hooked on heroin and worked as a prostitute in Glasgow to feed her habit.

She was last seen on April 4 2005 near a women's hostel in the Govanhill area, at around 11pm. Her body was discovered in woods near Roberton, Lanarkshire around a month later by a dog walker.

Detective Superintendent Willie Johnston said at the time: "My message to whoever did this is: 'We will not stop pursuing you, we will use every tool in the toolbox and every technique. We never go away'."

A 60ft image of the former horse-riding teacher, who spiralled into prostitution after her sister died of cancer, was beamed onto a tower block in Glasgow and the case appeared on Crimewatch.

Around 50 police worked on the investigation, nearly £4million was ploughed into chasing leads, and a £10,000 reward was offered.

After interviewing hundreds of witnesses, detectives became convinced a small number of Turkish men linked to a café in the city’s southside were responsible for the murder.

In an attempt to prove this theory, Strathclyde embarked on an intrusive surveillance operation that involved bugging the café.

Officers produced what they believed were incriminating translations of conversations and four Turkish men were arrested in August 2007.

However, the case dramatically collapsed after the transcripts were challenged by experts.

Oxford-based academic Professor Kerem Oktem, who had been hired by Strathclyde police to carry out a review, said: "We concluded that based on the material we were provided, the recordings, that it was not possible to make any conclusive statement about their involvement in the murder. It was simply not possible based on the material in the recordings."

One of the translators, Aksoy Ozer, also made a blistering internal statement alleging misconduct by officers on the case.

He claimed that had not been trained properly to use the equipment and claimed he had been asked to withhold details of the conversations he had picked up from the tapes.

He wrote: "[The officer] then told me not to mention this and to withhold this from the trial. I was extremely concerned regarding this as I had just been told to lie in court."

Further details of the troubled inquiry emerged in April following the revelation that a Scottish suspect, who had been interviewed six times and even admitted taking Emma to near the murder spot, had never been arrested.

Strathclyde had botched a high-profile murder investigation and its successor force, Police Scotland, then launched an illegal spying mission to flush out the suspected sources of a newspaper that exposed the flaws.

Ten years on, the Caldwell murder remains unsolved.