A close friend to Kate and Gerry McCann has revealed their heartache as German investigators prepare to drop the case into their daughter Madeleine's 2007 disappearance due to lack of evidence.

Lead prosecutor Hans Christian Wolters has warned that they may end their investigation after spending months trying decided on whether or not to charge Madeleine's prime suspect, Christian Brueckner.

"Of course we have an interest in keeping our suspect in custody," Wolters told the Sun.

"This gives us access to interrogations in the event of an indictment.

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"We have no endeavours to drag this out unnecessarily. We'll draw a line at some point and see."

It comes amid fears the prime suspect could be out of jail in days.

German authorities believe Christian Brueckner, pictured, is responsible for Madeleine McCann's disappearance. Photo / File
German authorities believe Christian Brueckner, pictured, is responsible for Madeleine McCann's disappearance. Photo / File

The convicted paedophile is currently in prison in Germany serving a sentence for drugs offences - and should be starting a seven-year jail term for the rape of an elderly American woman in Portugal in 2005.

But his lawyers have appealed the conviction on a legal technicality and the European Court of Justice is poised to give its verdict in two days' time.

A friend of the McCanns told the Daily Mail that they have had their hopes raised as a prime suspect was named — but are now preparing for the worst.

"It looks like the latest suspect could be ruled out because there is not sufficient evidence to charge him, which would be a huge embarrassment to the German authorities and very disappointing but not a total surprise to Kate and Gerry," the friend said.

"It had initially appeared such a vital and solid lead, and the breakthrough they had been dreaming of, but there seems to be a lack of any real evidence.

"Kate and Gerry have had their hopes raised and dashed so many times before. All they want is answers and to find out what happened to their daughter after more than 13 years.

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Madeleine McCann, pictured, went missing from her family's holiday accommodation in Praia Da Luz on the Algarve in May 2007. Photo / File
Madeleine McCann, pictured, went missing from her family's holiday accommodation in Praia Da Luz on the Algarve in May 2007. Photo / File

"It is a very frustrating and difficult time for them."

Last month, Wolters said he had "concrete proof" that Maddie, who vanished as a 3-year-old from a holiday apartment in Portugal in May 2007, had been murdered and that authorities are "convinced of his [Brueckner's] guilt".

He said he even knew how she had died but had no idea where her body was.

However, according to the family's ex-publicist Clarence Mitchell, Kate and Gerry McCann refuse to believe their daughter is dead until her body is found.

"Kate and Gerry want answers and while the Met are still treating Madeleine's abduction as a missing person rather than a murder inquiry it gives them a glimmer of hope. They will continue to hope until there is incontrovertible evidence which proves Madeleine is dead," Mitchell said.

Kate and Jerry McCann holding an image of what Madeleine would look like today at 16 - 13 years after going missing from Portugal. Photo / File
Kate and Jerry McCann holding an image of what Madeleine would look like today at 16 - 13 years after going missing from Portugal. Photo / File

Even if German authorities drop their inquiries into the latest suspect, the McCanns will still have hope as Scotland Yard will continue their search for Maddie.

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Their nine-year Operation Grange probe is set to get renewed Home Office funding to keep it going until at least spring next year.

Meanwhile, Portuguese police continue their search of remote disused wells near Praia da Luz, the resort Maddie vanished from, in hopes of finding Maddie's body.

Three have already been examined, with up to 20 more expected to be inspected in the coming days.