The prime suspect in the disappearance of Madeleine McCann was not interviewed by police in 2007 because he was not at home when officers knocked on his door, a former lead detective has claimed.
Christian Brückner was one of 600 people of interest investigated by police in the aftermath of Madeleine's disappearance, but officers sent to speak to the convicted paedophile returned with no information and never followed him up.
• 'He was hiding girl in cellar': Madeleine McCann suspect's chilling response to friends
• Madeleine McCann case: Letter from German authorities sparks confusion
• Madeleine McCann suspect moved to solitary confinement
• Madeleine McCann: Portuguese police refuse to share DNA evidence that could blow open investigation
In a television interview, Gonçalo Amaral the controversial police chief who blamed the McCanns for their daughter's disappearance, admitted it had not been possible to investigate every potential perpetrator in enough detail.
"I have been told that yes, that they had come knocking on the door. That person [Brückner] was not at home," he told TVI.
Amaral was taken off the McCann case over a series of crucial mistakes, including not securing the crime scene properly and launching a bungled investigation into Madeleine's parents, Kate and Gerry McCann, which was dropped after eight months.
Defending his force's missed opportunity with Brückner, Amaral said: "We are doing a survey of people known for theft, namely thefts in apartments. And apparently this man was not on the list of thefts in apartments – he had stolen fuel."
By May 2007, when Madeleine went missing, Brückner had spent eight months in prison for siphoning 321 litres of diesel from parked lorries in the nearby town of Portimao. He had one other charge of civil disobedience on his criminal record in Portugal.
But last week it emerged that, as he stood trial for the fuel theft, he told a judge he had historic child sex convictions in Germany from when he was a teenager.
This information was apparently never passed onto police, so the officers investigating Madeleine's disappearance had no idea that a convicted paedophile had been living less than 1.6km from the McCann apartment in Praia da Luz.
Amaral also claimed that Brückner was being made a "scapegoat", that German authorities have doctored photos of his campervan and that the McCanns were liars.
"He's an almost perfect suspect, or scapegoat," he said of Brückner. "All that's missing for him to become the perfect suspect is for him to be dead."
Asked whether he thought the German had taken Madeleine, he said: "To answer that question it has to be proven first that an abduction took place."
He also pointed to his own photo of Brückner's VW Westfalia campervan, covered in stickers and drawings on the side, which he claimed was taken in Portugal, adding: "I think it's important to ask why the photo put out by the authorities of the van was altered. Would that vehicle have gone unnoticed in Praia da Luz with those markings on it? I don't think so."
It was noted that the van may well have looked different in 2007.
Amaral again criticised Kate and Gerry McCann, saying: "All those people who were there lied. There was never a system for surveillance of the children who were sleeping in the apartments. They went to the apartments to use the toilet."
Those claims have been denied by the McCanns.
On Monday, it emerged that Brückner was also the registered owner of a white Mercedes-Benz 205D van and a grey Opel Ascona at the time Madeleine went missing. The whereabouts of both vehicles is unknown, but neither of them is thought to have been examined by forensic experts.
Brückner has now been linked to six vehicles, with only three having been searched by police. A large Winnebago was found to contain "countless children's items, most of them small swimsuits".