Rebelo has replaced Goncalo Amaral, the "oafish" local police chief out of his depth in a case that has captured unprecedented world attention, with millions fascinated by the story of the girl snatched from her bed on holiday while her parents ate with friends 200 yards away.

At a meeting, he accused some officers of having "closed minds" about who was guilty, saying that "pre-conceptions should be challenged".

In addition, he oversaw Operation Predator - raids on more than 70 suspected paedophiles, whose computers were searched last week for images of Madeleine or other evidence of criminal sexual acts.

Yet this medical practitioner had no intention of adhering to the ancient Hippocratic Oath.

Instead, arriving at Casa Pia (House of the Pious), a 17th century Lisbon orphanage where more than 4,000 children are cared for each year behind high stone walls, the doctor would summon selected boys and girls from their beds for examinations one night each week. After checking that the children were not suffering from any sexual infections, the doctor was joined by the orphanage caretaker, known as Bibi, who ushered the unfortunate children outside to a waiting van.

It is crucial for two reasons; first because it proves what international crime agencies have long suspected: that Portugal has become a magnet for predatory paedophiles from around the world, using the country's lax laws and preying on the high numbers of poor, abandoned children.

And second, because Paulo Rebelo, an urbane, methodical detective who led the Casa Pia paedophile inquiry, was last night finishing his first week as the new chief of the investigation into the disappearance of the British child.

Although by last night Rebelo had failed to make a breakthrough, sources say it is a clear sign, along with reports that Russian child traffickers may be involved, of a strand of his current thinking.

In a Lisbon café, an associate of Rebelo told the Mail: "The Casa Pia case had a deep affect on Paulo.

While the Mc Canns were warned repeatedly they faced jail for speaking about the case, he was been overheard, during his daily three-hour lunches of wine and shellfish, accusing the couple of killing their daughter.