COPS leading the new probe into the disappearance of Madeleine McCann fear their chances of solving the case have “slipped away”.
Christian B was revealed as the main suspect in a dramatic joint announcement by German and British police at the start of June.
However, yesterday a source close to German investigators admitted “momentum had been lost” in the probe.
German prosecutors had boasted that Christian B was their man and they had “concrete evidence” Madeleine was dead.
“In an investigation of this kind the first few weeks after the suspect’s name is released are absolutely vital,” our source told The Sun Online.
“Detectives remain convinced Christian B was involved in Madeleine’s disappearance but they still need that crucial part of the jigsaw.”
The suggestion that police are losing faith in the chances of arresting Christian B will devastate Madeleine’s parents Kate and Gerry.
However, faith remains in the investigation as German criminologist and profiler Mark T Hofman said he believes prosecutors have an “ace up their sleeves”.
Our source added: “The truth is, after a promising first few weeks where a lot of leads and information came in, tips have dried up.
“In recent days, for the first time since this investigation was publicised, those involved have been asking if their chance of nailing B has slipped away.
“The hope that he may also say something that incriminated himself from behind bars has also proved to be wishful thinking. He’s not said anything to a soul.”
Our source said Portuguese detectives, who have repeatedly clashed with their German counterparts, were privately “relieved”.
“The Portuguse officers have made it clear from the start they didn’t believe Christian B was involved,” he added.
“He was on the radar at the time and ruled out quickly.
“It would have been deeply embarrassing had it later turned out that Christian B was indeed the person who took Madeleine.”
Christian B, 43, is currently serving a 15-month sentence in his home country of Germany for drug offences.
The serial sex offender is also facing a separate sentence for the rape of a 72-year-old American woman on a waterfront villa less than a mile from where Madeleine went missing in Portugal in 2007.
Although he was convicted in December 2019, he appealed against his seven-year sentence and so it cannot be imposed until his appeal avenues are exhausted.
However, there remains hope that police may be able to bring a case against Christian B.
Mr Hofman said: “In my view, there is no doubt he was at the scene.
“Mobile phone data proves he was by the apartments. Also, his record fits the profile.
“I’m sure the prosecutor will pull an ace from up his sleeve and have more than we know so far.”
Hans Christian Wolters, the chief prosecutor in the case, has insisted that the Christian B is their man and they can place him at the scene.
However, no charges have yet been filed against Christian B, who has a record of sex offences and is now being linked to other missing children.
Madeleine is believed to have been snatched from the Ocean Club apartment where she was sleeping alongside her twin siblings Sean and Amelie on May 3, 2007, in Praia du Luz.
Described as a “twisted loner”, the sex offender is understood to have been a kind of drifter around the resort at the time.
Christian B was first linked to the Madeleine case after he allegedly made a drunken boast he snatched her while in a bar on the tenth anniversary of the crime.
Madeleine would have turned 17 last month, and the family have described the identification of Christian B as “potentially very significant”.
Experts have said Christian B matches the profile of a Jimmy Savile-style “paraphiliac”, who targets victims of all ages.
His ex-lawyer Serafim Vieira has described him as having “‘psychopathic traits” and admitted he could be responsible for Madeleine’s abduction.
Christian B had a rundown and dilapidated shack only two miles away from the McCann’s holiday let – and is known to have owned a mobile home he boasted could carry “drugs and children”.
However, a series of bungles in the police investigation have cast doubt over whether prosecutors can secure a conviction.