No trace of Charlene Downes has ever been found
The police watchdog has condemned Lancashire Police's handling over a murder case of a missing girl and said seven officers should be disciplined.
Charlene Downes, 14, of Blackpool, went missing in 2003. Two men were charged over her death but later acquitted.
The Independent Police Complaints Commission (IPCC) said police errors in gathering evidence had contributed to the collapse of a retrial in 2008.
Charlene's body has never been found and nobody was ever convicted.
'Catalogue of errors'
Lancashire Police's investigation into the schoolgirl's disappearance was "handled poorly and unprofessionally", the IPCC said.
It said it had found a "catalogue of errors which undermined the court case". There was no immediate comment from Lancashire police.
The teenager had been with friends at a bar when she vanished on 1 November 2003.
Iyad Albattikhi was accused of murder and Mohammed Raveshi was charged with assisting an offender by disposing of a body.
In May 2007, a jury failed to reach a verdict and a retrial was ordered.
The two men were cleared because the prosecution found a "number of issues" with the way audio and video covert evidence had been collected by officers.
Ass Chf Con Andy Cooke, of Lancashire Police, said: "It is clear that certain aspects of the case have not been well managed - specifically during the time prior to the trial, and for this we must certainly apologise to the Downes family."
The police chief admitted lessons had been learnt from Charlene's case which remains a "live investigation".
The police watchdog has now recommended that one officer should face a disciplinary hearing and another should receive a written warning. Five other officers should receive words of advice, it said.
Meanwhile two officers, who have since retired but who had worked on the case, cannot be considered for disciplinary action.
However, the role of another retired officer who worked in a civilian capacity should be looked at, the IPCC said.
Naseem Malik, IPCC Commissioner for the north west, said: "This is a very sensitive area as, by the very nature of the business, the techniques used must remain secret.
"But what is abundantly clear is that the covert surveillance aspect of Lancashire Constabulary's investigation into Charlene's disappearance was handled poorly and unprofessionally."