Black – serving 12 life sentences for the kidnap and murder of four British girls – has long been suspected of killing seven-year-old Mary Boyle here.
Cold case expert Chris Clark has found evidence that the sex predator went back to the area in County Donegal the next year searching for another victim.
That comes as prosecutors consider whether to charge Black with the murder of Genette Tate, 13, of Aylesbeare, Devon, in 1978. Her body has never been found.
Mary vanished in Cashelard in March 1977. Former detective Clark says he has evidence van driver Black was working in the area at the time.
Clark said Black returned in 1978, raising fears he was hunting for another victim.
“There is confirmation that when Mary went missing Black was a regular visitor at a pub in County Donegal. He appears on a Garda charge sheet for after hours drinking,” he said.
“His presence was additionally recorded in the area a year after Mary went missing. He was noted by female witnesses asking about another girl. When they declined to help, they described him as becoming angry.
“He was noted by female witnesses asking about another girl. When they declined to help, they described him as becoming angry.”
Grangemouth-born Black, 67, was found guilty in 1994 of three child murders in the 80s.
His reign of terror ended in 1990 when he was caught with a girl of six stuffed in a sleeping bag in his van in the Scottish village of Stow.
He raped and murdered 11-year-old Northumberland schoolgirl Susan Maxwell in 1981.
She was dumped in Staffordshire.
Five-year-old Caroline Hogg was abducted in Portobello, Edinburgh, and killed in 1983. Her naked remains were found 10 days later in Leicestershire.
He picked up Sarah Harper, 10, in Leeds in 1986 then raped and murdered her. He dropped her body into the River Trent.
In 2011, Black was convicted of kidnapping and murdering Jennifer Cardy, nine, who was snatched in County Antrim, Northern Ireland, in 1981.