Police hope Black may be persuaded to confess to murders they suspect he has committed since the late 1960s. But the length of time and the difficulties in assembling a coherent prosecution case means it is unlikely he will stand trial for any of the killings - even if he admits them.
Police officers who have investigated his background since his arrest in 1990, are confident that he could be questioned about at least six or seven cases which remain unsolved in England, one or two in Northern Ireland and three in France.
It may well be that Black has killed even more children, but estimates of at least 19 have been discounted by police sources.
The difficulty facing the police, if they are unable to trace Black's whereabouts through receipts indicating his movements in the areas where the outstanding murders took place, is the unlikelihood of any confession from Black.
His remark to the police of 'Well done, boys' as he left the dock yesterday was sneering comment on their inquiries so far - to which he has given no help.
Top of the police list will be the the disappearance, on 19 August 1978, of Genette Tate, 13, who vanished while on her newspaper round in Aylesbeare, Devon. Her body was never found, only her bicycle left lying in a country lane.
At the time there was speculation that Genette had been knocked down by a car and her body then hidden. The teenager was last seen cycling through her home village. She stopped to talk to two friends and then rode on and was never seen again.
There are at least another three girls whose disappearance might be laid against Black:
April Fabb, 13, vanished in 1969 while cycling in her home village of Metton in Norfolk, a county Black visited regularly. Her bicycle was found in a field 600 yards away from her home. Her body was never traced. Norfolk police have already spoken with the Lothian and Borders force about her disappearance.
Christine Markham, 9, disappeared on her way home from school in Scunthorpe, Humberside, in May 1973. Black will almost certainly be interviewed by the Humberside force about her.
Colette Aram, 16, was a trainee hairdresser who vanished on 30 October 1983. She was walking to see some friends in Keyworth, Nottinghamshire, when she was grabbed. She was found strangled and sexually assaulted in a field a mile away the next day.
The police will talk to Black about two or three other child murders in England - the details of which have not been disclosed - and two cases of missing children in County Antrim in Northern Ireland.
The French police are known to have made contact with British detectives concerning Black's movements in France during the 1980s, although Lothian and Borders police refuse to discuss the contacts.
Three French children, who have not been named, are all thought to have been kidnapped and killed in remote areas and the French authorities are anxious to know whether Black has been pinpointed in any area close by. It is known that Black had access to a caravan in France and regularly travelled through the country during the 1980s, possibly to visit the Dordogne home of the London family with whom he lodged for many years.
Black was always keen to make long-distance poster deliveries on behalf of the London company where he worked. He also travelled to the Netherlands and Denmark, usually to collect child pornographic magazines and video films not obtainable in this country.
The prosecution's case against Black was, in part, based on the fact that he had already abducted a six-year-old girl in the Scottish borders in 1990 in exactly the same way that the three other girls, Susan Maxwell, Caroline Hogg and Sarah Harper were kidnapped.
The case was built on the meticulous collection of evidence covering Black's movements throughout Britain between July 1982, when Susan Maxwell was abducted, and 1990, when a girl called Teresa Thornhill, then 15, was almost kidnapped and killed by Black.
The same techniques could now be used to build a case against him for the unsolved murders.
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