Charlene Downes' body has never been found
An investigation into a missing schoolgirl in Lancashire has been referred to the police watchdog after a man accused of killing her was cleared.
Charlene Downes, 14, from Blackpool, was last seen in November 2003.
The decision to formally clear the murder accused, who cannot be named, was taken on the judge's directions at Preston Crown Court on Wednesday.
Lancashire Police have now referred the case to the Independent Police Complaints Commission (IPCC).
Chris Weigh, Assistant Chief Constable of Lancashire Police, said: "We want to be clear about why we find ourselves in the position where the prosecution had to be halted and if there are lessons to be learned, we will learn from them.
"We must not forget in all of this that there is a family who need to know what has happened to their daughter.
"Charlene's parents cannot rest until they feel that justice has been done and we will continue to support them as the investigation progresses."
Another man, Mohammed Raveshi, 50, who was accused of helping to dispose of the girl's body, was also formally cleared.
It was the second trial the men faced after a previous jury failed to reach a verdict in May 2007.
Mr Justice Roderick Evans issued the directions after submissions from defence barristers on Wednesday.
Karen Downes, Charlene's mother, said she was "absolutely devastated" by the decision.
She added: "Part of me went with her. She did not deserve to die."
Mr Raveshi, who was charged with assisting an offender, spent two-and-a-half years in jail on remand.
Mohammed Raveshi spent more than two years on remand
"I am very relieved this is over, but everything what happened - being in jail for something you have no knowledge of, I made it very clear from the start," he said.
The inquiry was one of Lancashire's longest-running investigations involving a child missing from home before detectives switched the focus to a murder hunt.
No trace of Charlene has ever been found. Bob Marshall, Chief Crown Prosecutor for Lancashire, said: "This was always a very difficult case because Charlene literally disappeared without trace.
"In spite of the inherent difficulties we have worked hard to build a case which was strong enough to put before a jury.
"However, recent developments have left us with grave doubts about the reliability of some of the evidence upon which the prosecution case would have been based."