THE police case against the prime suspect in Madeleine McCann’s disappearance appeared close to collapse last night.

       An ex-pal of Christian B, 45, made a damning statement against the convicted child sex fiend.

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       The damning statement by Helge B — an old pal of Christian B — has become a cornerstone of the German-led police case but he is said to be backing out of helping Credit: The Sun 4

       The key witness said Christian B claimed 'she didn't scream' as the pair discussed Madeleine's case over beers Credit: BILD

       But sources close to the German probe say their key witness is “wobbling” and threatening to stop helping.

       Cops hope to nab Christian B over Madeleine, who vanished in 2007 aged three.

       A damning statement by Helge B — an old pal of Christian B — has become a cornerstone of the German-led police case.

       But sources close to the investigation warn he could soon back out and refuse to support his claims in court.

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       A German source told The Sun: “Word is that Helge B is about to withdraw his evidence.

       “He was paid a huge sum to repeat his statement in a German newspaper and now he’s pulling the plug.

       “It just goes to show you what type of people you are dealing with — and their credibility as witnesses.”

       Helge B’s move could be the final blow in the stalling bid to bring Christian B to court for the suspected abduction and murder of three-year-old Madeleine in Portugal in 2007.

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       It will be another setback for her parents Gerry and Kate, both 55, of Rothley, Leics.

       German Helge B, 48, was a criminal pal of drifter Christian B when they lived on the Algarve around the time of Madeleine’s disappearance from her holiday apartment in Praia da Luz.

       He told cops he was chilled by Christian B’s alleged dark confession when the pair met at a music festival in Spain a short time after the tot vanished.

       As the pair discussed the case over beers, Christian B was said to have coolly confided: “She didn’t scream.”

       The convicted rapist and child sex attacker clearly implied he had taken Madeleine, Helge B told cops.

       McCann probe prosecutor Hans Christian Wolters said he was unaware of Helge B's suspected change of heart — but insisted his statement would still carry weight.

       He said: “Anyone who has said something must be measured by it. Witnesses are subject to the duty of truth — they have to testify. You can’t just choose something like that.”

       Helge B's threats to back out came as it was revealed Christian B has written begging letters to pals asking them to back him if he goes on trial.

       He faces new charges of rape and child sex offences unconnected to the McCann case.

       In one letter, the sex offender moaned that prosecutors were making him out to be “a monster”.

       An ex pal said: “I know of two people on the Algarve who got the messages. It really freaked them out.”

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       The dramatic move could be the final blow in the bid to bring Christian B to court for the suspected abduction and murder of three-year-old Madeleine in Portugal in 2007 Credit: PA 4

       The news will be another setback for her parents Gerry and Kate Credit: PA

       Christian B is currently in jail in Germany for the 2005 rape of a 72-year-old American woman in Praia da Luz.

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       Detectives claim to have “concrete evidence” that Madeleine is dead but have yet to produce further material which could lead to a charge.

       Christian B’s lawyer, Friedrich Fulscher declined to comment last night.