Scientist and former South African police colonel Danie Krugel secretly flew out to Portugal to meet the couple before spending a week tracking the four-year-old's DNA trail.
Using cutting-edge technology, Krugel led Portuguese police to an area of beach 500 yards from where she vanished.
Detectives took his finding so seriously that they sealed off the entire area.
But in what could turn out to be yet another astonishing bungle, Portuguese police never bothered to dig at the spot.
Now, as sacked police chief Goncalo Amaral is off the inquiry and a new officer, Carlos do Carmo - dubbed "Portugal's Robocop" - takes over, Krugel is heading back to reinvestigate.
A source close to the McCanns said last night: "Kate and Gerry are pleased he's returning. They worked with him before and want to see his leads investigated."
The former South African detective has an amazing 90 per cent success rate in tracing missing people.
Speaking exclusively to the Sunday Mirror, he said last night: "I'm preparing to fly to Portugal again because the investigation seems to have come to a halt.
"I'm convinced Madeleine's body is in Praia Da Luz."
The McCanns turned to him in July to spend a week investigating Madeleine's disappearance after being deluged with emails from members of the public recommending him as a "genius".
He said: "Gerry sent me a strand of Madeleine's hair for DNA purposes, which had been removed from her coat."
Krugel became a household name in South Africa when he created a DNA tracking device which solved a 19-year mystery about the whereabouts of six schoolgirls snatched by a paedophile.
He told last night how he used the same method to track a potential burial spot for Madeleine on the beach in Praia da Luz.
The area was sealed off and Krugel suggested sniffer dogs be brought in to further pinpoint the spot where they needed to dig. Yet ironically, when the dogs arrived they were used by cops to turn the finger of suspicion on to Gerry and Kate.
Portuguese police were more excited about the dogs' reaction when they searched the McCanns' Ocean Club apartment and hire car.
It means the area on the beach has still not been searched properly by officers and no dig has ever taken place.
And it came amid new reports from Portuguese newspaper Correio yesterday claiming police believe Madeleine was buried on the beach in Praia da Luz soon after her death.
Krugel added: "After I conducted my investigation I gave the police a map pinpointing the spot I think Madeleine is. And I handed over a 2,000 word report on what they should do next.
"I said sniffer dogs should be brought in to start the search. But I warned that this alone was not enough as dogs are only a success in missing person hunts three out of four times.
"That is why I also suggested a fingertip search of the area and a dig of the spot I located. But if this has not been done, the police really need to start from scratch and investigate that area again."
He added: "Too much time has been wasted accusing Kate and Gerry and not enough has been spent searching for Madeleine and following up on leads."
Krugel's device apparently combines quantum physics and global positioning technology to pin-point a body on a map.
His invention has already helped solve the riddle of a man reported missing by his family.
South African cops had no clue where he was - until Krugel was called in.