German and Portuguese are continuing to work on the case of Madeleine McCann (Image: PA)

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Police probing Madeleine McCann’s disappearance are launching a push to find the “missing piece of the jigsaw” that could snare the main suspect.

German and Portuguese investigators are to carry out new interviews of key witnesses in the Algarve who knew paedophile Christian Brueckner.

Experts described it as “a very important step forward” and raised hopes it could lead to Brueckner being quizzed and even charged.

A second top-level summit between German, British and Portuguese detectives is also expected to take place in Lisbon this spring.

Prosecutors hope a new clue will give them what they need to directly question Brueckner about the case.

He was named as the prime suspect last year but is yet to be quizzed about her 2007 disappearance.

(Image: Carabinieri Milano via Getty Ima)

Brueckner is currently serving a seven-year term in a prison in Hanover for raping a pensioner in Praia da Luz in 2005.

A well-placed source said: “The police have already put some witnesses on standby to sit down for new interviews.

"There is a real sense of new year, new hunt for clues. It’s very much in everyone’s minds to get the case cracked.

“There’s a missing piece of the jigsaw still out there somewhere.”

VANISHED

A secret summit took place in Lisbon last summer between detectives from Scotland Yard, the Policia Judiciaria and Bundeskriminalamt.

They met to “fine-tune” Brueckner’s profile in a bid to discover where Madeleine’s body could be buried.

German detectives have also spent time quizzing key witnesses in the Algarve, including Mr Brueckner’s British ex-girlfriend.

A former allotment of Brueckner's was dug up last July
(Image: Getty Images)

Madeleine vanished from her parents’ holiday apartment at the Ocean Club complex in Praia da Luz in May 2007.

Parents Gerry and Kate McCann had left the three-year-old alone with her twin siblings while they dined with friends at the nearby tapas restaurant.

German authorities say they are sure Brueckner abducted and murdered her but have declined to say what evidence they have.

Prosecutor Hans Christian Wolters recently admitted that without new clues, the 43-year-old will never be quizzed over Madeleine.

Brueckner’s lawyer Friedrich Fulscher insists that the German has nothing to do with the youngster’s disappearance.

The McCanns, of Rothley, Leicestershire, have refused to give up hope that she could still be alive.