It was one of the biggest investigations in the history of Lancashire Police and certainly one of the most high profile.
On November 1, 2003, Charlene Downes vanished without trace.
The 14-year-old schoolgirl had been with friends on the last night she was seen alive and had promised her mum, Karen, that she wouldn't be home late.
The storybehind her disappearance is examined in a Channel 5 documentary The Murder Of Charlene Downes.
The Saturday Charlene disappeared had been like any other, she had been given her pocket money - £5 - and headed out to the arcades with his sister, Becky.
Karen will never forget the final words she said to her young daughter, who would now be 30.
The devastated mum explained: "I said to her 'don't be late home my darling'.
"And she replied, 'mum, I won't be home late'."
Officers spoke to thousands of people and undercovered the dark, seedy underbelly to the seaside resort of Blackpool.
They found teenage girls were "swapping sex for food, cigarettes and affection" in what one detective described as "endemic child abuse".
But when it came to finding the teenager, all they were coming up against were brick walls.
One of the officers who worked on the case, Detective Don Fraser, said: "It became very difficult to see the wood for the trees. Girls of Charlene's age were reluctant to tell the truth.
"They thought it best to tell a white lie to protect their own reputation."
Then they were given what they thought was an unbelievable breakthrough.
Local businessman, David Cassidy, came forward to say he knew what had happened to Charlene.
He told police that he had been told the 14-year-old had been murdered and her body disposed of - and that he knew who'd carried out the gruesome crime.
Cassidy pointed the figure at two kebab shop owners, Iyad Albattikhi and Mohammed Reveshi, and claims he was told what had happened by one of the men's brothers.
Seemingly it was the breakthrough police needed to finally crack the case.
Albattikhi and Reveshi were brought in for questioning and their homes and cars put under covert surveillance.
And when the 52 tapes, which contained four weeks worth of conversations, were analysed by Det Sgt Jan Beasant and she came back with her findings, it seemed like an open and shut case.
Albattikhi was charged with the murder of Charlene Downes and Reveshi with disposing of her body.
The two men's trial started in May, 2007, but the jury failed to reach a verdict.
A retrial was ordered and scheduled to take place in April 2008.
But this had to be abandoned by the Crown Prosecution Service because of "serious errors" in the covert surveillance that had been used as evidence.
Albattikhi and Reveshi were released.
How did Lancashire Police get the huge investigation so wrong?
First, there were huge issues with the quality of the covert surveillance.
Don Fraser admitted: "The audio was very poor, disturbingly so.
"One of the microphones had been placed very close to a TVand this hampered the recording."
Jan Beasant, the officer who spent 18 months listening to the tapes and producing the transcripts that formed the backbone of the prosecution's case, is adamant that what she heard in them is correct.
She says Reveshi is feeling the pressure of the investigation and says in one muffled recording: "They will find something here so I'm going to check the burial place."
The two men can then be heard discussing "big bones".
Beasant hears Reveshi say: "the big bones went into the machine as well, you know that, don't you?"
Cassidly had claimed Albattikhi had murdered Charlene and Reveshi had helped him dispose of her body by turning her into kebab meat.
The recordings and the transcripts were read out in court with Charlene's family present.
Her devastated mum, Karen, said: "The stuff that came out in that court was just horrendous."
But forensic audiologist Elizabeth McClelland says Beasant's transcripts should never have been used in the trial.
She explained: "This is a classic case of cognitive priming. The evidence presented by Jan Beasant was potentially misleading.
"It's extremely important that when recordings are transcribed that the person transcribing them has no prior awareness at all about that evidence.
"In this case it shows several signs that she was subject to bias and influence by the events that she was investigating."
Devastatingly, McClelland hears something very different when she listens to the tapes.
She is adamant Reveshi doesn't say the words "burial place" and says the "big bones" discussion could easily be related to something going on in the background.
Then there's the "second pillar" the case against Albattikhi and Reveshi is based on - David Cassidy's testimony.
After his initially came to police, Cassidy was provided with a covert recording device and told to speak to Albattikhi's brother, who he says originally told him about the murder, and get him to repeat the allegations - but this time on tape.
Cassidy did speak to the brother for a second time - and he denied ever making the claims.
But police insisted they had never heard - or even seen - this tape.
Don Fraser said: "To say my heart sank when I heard this tape is an understatement.
"I didn't know anything about these CDs from 2005 I haven't got a clue what happened.
"I'm baffled by what happened and why."
But when the recording emerged, it was a gift to the defence, who reportedly "punched the air" when they were revealed.
The re-trial collapsed before it had begun as the prosecution no longer had any case to bring with the two pillars it was based on being discredited.
In the aftermath the Independent Police Complaints Commission launched an investigation into what had gone wrong.
Jan Beasant was found guilty of misconduct but this decision as overturned by the Police Arbitration Tribunal and she mantains that her transcripts of the covert surveillance were accurate.
- The Murder of Charlene Downes is on Channel 5 at 9pm tonight, tomorrow and Thursday.
