Officers arranged for a man to pose as a prisoner in order to befriend Christian Brueckner behind bars, according to the Mirror. However, they were unable to tease a confession out of the inmate.

       The failed sting was said to have taken place after one of his former friends came forward to claim that Brueckner had admitted to having been involved in Madeleine’s disappearance.

       Helge Busching – who met Brueckner in the Algarve in Portugal – told German police that in 2008 Brueckner had said he had a hand in it.

       The paper said that Busching’s information was convincing enough to investigators that they decided to infiltrate Brueckner’s Wolfenbüttel jail.

       However, police were reportedly unable to get him to confess to anything.

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       Prosecutors in Braunschweig told the Mirror they had “no comment” when asked about the undercover operation.

       Madeleine’s disappearance in the resort of Praia da Luz, Portugal in 2007 sparked one of the largest missing persons investigations ever.

       However, no trace has ever been found of the child.

       To this day, Madeleine’s whereabouts remain unknown.

       But last year, German prosecutors said they assumed the girl was dead.

       Madeleine was on holiday with her parents, Kate and Gerry McCann and her siblings when her disappearance had occurred.

       She and the other children had been left asleep in the couple’s ground-floor apartment on May 3 that year.

       Her parents checked in on the children throughout the evening, until Kate discovered Madeleine was missing at around 10pm.

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       Brueckner was named as the prime suspect in Madeleine’s disappearance in June 2020.

       It came after analysis of mobile phone records placed him in the holiday resort on the same night she disappeared.

       German prosecutors told the Mirror in October that they were “100 percent sure” Brueckner had murdered Madeleine.

       Hans Christian Wolters said: “We’re confident we have the man who took and killed her.”

       He added: “It is now possible that we could charge. We have that evidence now.

       “But it’s not just about charging him – we want to charge him with the best body of evidence possible.

       “When we still have questions, it would be nonsense to charge rather than wait for the answers that could strengthen our position.

       “That’s why we said we’ll investigate as long as there are leads or information for us to pursue. I’m not saying that what we have is insufficient now. But he’s in prison, so we don’t have this pressure on us. We have time on our hands.”

       Brueckner is currently serving a sentence for the rape of a 72-year-old American woman in Portugal in 2005.