Ronald Castree, 54, of Shaw, Oldham, was convicted at Bradford Crown Court by a jury which heard how he abducted the schoolgirl as she went on an errand in Rochdale, Greater Manchester, on October 5, 1975.
Tax clerk Stefan Kiszko spent 16 years in prison for Lesley's murder but was released in 1992 after his conviction was quashed.
The release of Stefan Kiszko in 1992 reignited the question of who did kill Lesley Molseed.
Speculation at the time about who did it ranged from notorious serial killers such as child-murderer Robert Black and Yorkshire Ripper Peter Sutcliffe to people from the local community in Rochdale.
Even before the Appeal Court's final decision on Mr Kiszko in 1992, West Yorkshire Police reopened their murder inquiry.
Lesley's own stepfather Daniel Molseed was forced to publicly declare his innocence after confirming he had been arrested and questioned 16 years after her death.
A convicted paedophile called Raymond Hewlett was a much more serious suspect. In September 1972 Hewlett abducted a 12-year-old girl and took her on to moors near his home in Todmorden, West Yorkshire.
He incapacitated her with a rag soaked in paint thinners and she only escaped being raped after he ejaculated prematurely.
In 1978 Hewlett attacked another girl, this time putting a gun to her back but she managed to convince him visitors were arriving imminently and her let her go.
After Mr Kiszko's release, Hewlett was interviewed about Lesley's death and a file was sent to the Director of Public Prosecutions but it was decided there was not enough evidence to proceed.
In 1997 a book was published jointly written by a local journalist, a former police officer and a lawyer which named Hewlett as Lesley's killer.
The book was serialised in a national newspaper and in 1999 Lesley's family said they intended to bring a private prosecution against him.
That same year, however, saw the start of a new forensic examination of the evidence which had been retained from the 1975 crime scene.
Lesley's clothing had been destroyed in 1985, as was routine. But strips of adhesive tape had been kept which had been used to remove fibres from the inside and outside of Lesley's semen stained pants.
Scientists from the Forensic Science Service's lab in Wetherby, West Yorkshire, managed to extract sperm heads from this tape. And from these sperm heads, a DNA profile of the man who ejaculated into Lesley's pants was obtained.
Armed with this powerful new piece of information West Yorkshire Police again announced it was officially relaunching the inquiry using a dedicated team of officers and the Holmes major incident computer, which was not available to the original investigation team.
The DNA profile again proved conclusively it could not have been Stefan Kiszko's semen.
It also meant the elimination of a large number of others suspects.
These included Hewlett, who was "categorically ruled out" when detectives found a sample of his DNA despite being unable to trace him.
It also ruled out many of the notorious serial killers whose names had been linked to the murder over the years. Ronald Castree was arrested in Oldham in 2005 in relation to an incident "unrelated and irrelevant" to Lesley's murder.
As is routine, police took a swab from him for DNA analysis. This was later compared with the profile obtained from the sperm heads found in Lesley's pants and there was a complete match.
According to the science of DNA analysis, the chance of this profile matching someone other than Castree was in the order of one in a billion.
Castree was arrested on November 5 last year. He had no explanation for how his semen got on to the inside of Lesley's underwear.
But Raymond Hewlett, who is thought to be abroad and could not be traced by police, had one final part to play in the Lesley Molseed's tragic story. Castree, through his lawyer, told his trial it was "overwhelmingly probable" that Hewlett was the killer.
The jury did not agree.
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