Madeleine McCann was kidnapped by an accomplice and sold to the main suspect, a prosecutor building the case against him has suggested.
Paedophile Christian Brueckner is currently serving a seven-year jail term for raping a pensioner in Praia da Luz, the Portuguese resort from which Madeleine went missing in 2007.
Last month, the 45-year-old was made an "arguido" – which translates as "named suspect", "formal suspect" or "person of interest" – by Portuguese authorities in the disappearance of little Madeleine.
German prosecutor Hans Christian Wolters told Portugal TV investigator Sandra Felgueiras he could not comment on the speculation.
When she pressed Mr Wolters on if Madeleine was sold to the suspect, he replied "Maybe, it’s a possibility."
Madeleine McCann disappeared 15 years ago
Madeleine disappeared in May 2007 from an apartment during a family holiday.
Brueckner denies having any involvement in the disappearance of Madeleine.
This week it emerged that Brueckner is now reportedly writing a "bestseller" behind bars at a high-security prison in Oldenburg, northwest Germany, the Olive Press reports.
Madeleine's parents Kate and Gerry McCann
The Spanish news outlet says a six-page letter was written to an American blogger by the suspect where he insists his book will be a "bestseller" better than any John Grisham novel.
Brueckner also allegedly wrote he was the world's most famous German, adding that "Hitler was Austrian".
Brueckner was named an "arguido" by Portuguese authorities last month, in a move that is said to be linked to the 15th anniversary of Madeleine's disappearance.
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This has important legal ramifications, because whilst in Germany there is no time limit for a murder charge, in Portugal, there is a strict 15-year limit.
He was first named in the summer of 2020 as a prime suspect by German police after mobile phone records placed him in Praia da Luz on the night Maddie vanished.
But despite further extensive inquiries he has never been charged.
Recently, the Portuguese authorities confirmed that they will continue their inquiries amid reports that Scotland Yard’s Operation Grange investigation will be wound up this autumn.
Brueckner also still faces charges for the rape of an Irish national in Portugal in 2004.