Genette Tate, who disappeared during a newspaper round on the afternoon of August 19, 1978, is Britain's longest running missing persons inquiry.

Genette's blue bicycle and newspapers were found in narrow lane in Aylesbeare, Devon, minutes after she spoke to two friends.

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The 13-year-old had only carried out the newspaper round because she was filling in for the regular paper boy who was on holiday.

Devon and Cornwall police has pledged to keep their murder-style inquiry open until the riddle of her mysterious disappearance is solved.

Speaking before the 20th anniversary of Genette's disappearance her mother, Sheila Cook, said: "I do feel there is someone out there with something to tell - and I still feel we will get the answer."

Mrs Cook, who re-married 17 years ago, accepted years ago her daughter was no longer alive but she still wants to "put Genette to rest".

She said: "I do not know whether I want the answer - I do not know whether I could cope with the detail."

Fresh appeal

Mrs Cook said: "In the past couple of years I have been very aware she would have been a mature person.

"And there are little landmarks - hopefully I would have been a grandmother - and you suddenly realise the enormity of the life which is lost.

"I am more sad than I used to be, I do not know whether that is my age making me more reflective, or thinking about what might have been."

The head of Devon and Cornwall police CID, acting Assistant Chief Constable John Essery has made a fresh appeal for information because someone still may be covering for an individual out of "misguided loyalty".

Child killer could hold key

Detective Constable Phil Diss, a member of the original inquiry team of 300 officers, said: "It is the great mystery certainly of my career and other senior officers.

"I would dearly love to see it brought to a conclusion."

Genette's father, John Tate, is convinced child killer Robert Black, currently serving at least 35 years for murdering three girls in the 1980s, holds the key to Genette's disappearance.

According to police, in 1978 Black regularly used a red Ford Transit van in his job as a poster deliverer, which would have on occasions taken him to Exeter.

Minutes before Genette is believed to have disappeared, a similar vehicle was seen travelling at speed from Aylesbeare but was never traced.

Child killer 'not eliminated'

In 1996 a witness told police she recognised Black from a newspaper photograph as the man she had seen leaning on a red Transit-style van at Exeter airport, not far from Aylesbeare, on the day Genette vanished.

The woman said he had been watching her children and she saw him drive off towards Aylesbeare.

Black was interviewed by police in 1996 and in February this year about Genette's disappearance, but denied involvement with her.

Police inquiries have failed to put him in Aylesbeare at the time of the disappearance but he has not been eliminated from the investigation.