Were it not for coronavirus, Graham Hill would be in the US this week training FBI agents. His speciality is the abduction and murder of children by sexual predators, and when he talks, senior detectives from police and investigation agencies around the world listen.
But they didn't in the Portuguese holiday resort of Praia da Luz in 2007.
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Hill has given the Daily Mail a disturbing insider account of the chaotic first two weeks of the hunt for Madeleine McCann.
On May 7, 2007, Hill – then a Surrey detective superintendent seconded to the UK's new Child Exploitation and Online Protection centre – flew to Portugal to lend expert help to the hunt for Madeleine.
The 3-year-old's disappearance on May 3 from a bedroom at the Ocean Club while her parents, Gerry and Kate, ate dinner was beginning to dominate the news.
Detective Superintendent Hill – who had secured the world's first conviction based on familial DNA – could have helped while the evidence was still fresh.
But because of systemic dysfunction and suspicion of outside intervention by the Portuguese police team – led by detective Goncalo Amaral, who would be removed from the case and publish a book which made false allegations against Madeleine's parents – his input was unwelcome.
Thirteen years and £12 million of UK taxpayer-funded investigations later she has still not been found.
But 10 days ago, German prosecutors named convicted paedophile Christian Brueckner, 43, as a prime suspect.
He is serving a jail term in Germany for drug-dealing. In December he was sentenced to seven years for raping a 72-year-old US woman in Praia da Luz in 2005 – a conviction that is being reviewed.
The blame game has already begun, however. Why wasn't Brueckner on the radar of the initial Portuguese investigation, and why wasn't he identified by the Met's own nine-year probe – Operation Grange?
A source close to the McCann case said last night: "A war is brewing between the Portuguese police and Scotland Yard over their previous knowledge of Brueckner. The Portuguese are, once again, becoming defensive about their role."
Portuguese police have told local media that Met detectives knew about Brueckner in 2012 but had "devalued'"him as a suspect by not "attributing relevance" and "never" requesting further information.
A British police source confirmed Brueckner was a "person of interest" at the start of Operation Grange, but there was insufficient evidence to make him a suspect.
Hill, who retired from the force in 2012, has watched the latest development with interest.
On the day he arrived in Praia da Luz in 2007 he met the McCanns, who told him they were already concerned about what was being done by local police.
He said: "They wanted reassurance. Gerry McCann told me, 'I took my daughter from one EU country to another EU country. How could the standards of police investigation be so different?'.
"I could not give them any reassurance. But I said I would try to help them find their daughter."
The next morning at the town's police station he met those leading the Portuguese investigators.
"It was like going back to the 1970s," he recalls. "Very macho. The incident room was full of cigarette smoke and there was a noticeable absence of women.
"It wasn't what I expected coming from a UK investigative perspective. There did not seem to be a lot of people around. It wasn't very busy. And that's all I saw of how they worked. I was never invited anywhere else.
"It was fraught from the word go. The detectives were very polite and measured but also suspicious of why we were there and what we were seeking to achieve. I only met Amaral on that first occasion and one further meeting. Clearly he felt he did not need my help."
Hill said he asked every day for information or a meeting with someone connected to the case.
"I had to do all the pushing. The meeting would be scheduled then, invariably, cancelled.
"If I asked about search strategies they would simply tell me they were doing everything possible. If I asked about known sex offenders they would tell me it was all in hand. I was kept at a distance. I could offer advice on predatory sex offenders and hope they would show some interest and engage, but they didn't.
"It took an awfully long time to establish even the smallest detail.
"No one ever said, 'What do you think?'. They were simply paying lip service to my presence."
It was several days before they even told him they were focused on a prime suspect – British expat Robert Murat. Hill offered them advice on interview techniques, which was the only time he believes they ever really listened to him, but Murat proved to be completely innocent.
No other suspects were ever mentioned to him. The McCanns only became suspects, or "arguidos", in September – another indication of how the investigation was run badly from the start.
Hill said that had Portuguese detectives been more willing to discuss the case "I would have told them the first people they needed to eliminate from the investigation is the parents or a relative". He added: "For the Portuguese to make them suspects months later was complete nonsense.
"The job had got away from them very early on and they never recovered. It was too big for them."
After 10 days of passive obstruction, Hill returned to the UK.
Difficult questions must be asked of Portuguese and British police, he said, as to why Brueckner was not properly investigated before now. He added: "When did the Portuguese know about Brueckner? And in what context? These same questions apply to the Metropolitan Police.
"The worst-case scenario for any senior investigating officer is that there is information already in their systems which would have led to an ID of the offender."
Citing US research, he said: "They looked at 75 convictions for child abduction – 70 per cent of those who carried them out were spoken to in the first 48 hours of the investigation.
"It's good to say, 'Let's go back and look again'. But that didn't happen. Madeleine still has not been found. But we must learn lessons from her case."