Police Have Been Investigating Prime Suspect In Madeleine McCann Case For Four Years

German prosecutor Hans Christian Wolters and Scotland Yard launched a public appeal for any information about the man last year.

But the man, who has only been identified Christian B due to privacy laws, had been on their radar for a lot longer.

Wolters said: "By that time Christian B had been under investigation already for three years. We did not take the decision to go public lightly.

"Since then we have found a lot more pieces of the puzzle, but I cannot reveal what they are. We are making progress and have the same number of investigators working on the case, but we don't yet have enough to charge the suspect."

He added: "There is no time limit to our investigation, but we won't keep it going forever."

Forty-three-year-old Christian B is reported to have been living in Portugal at the time of Madeleine's disappearance in 2007.

His mobile phone was found to be in use nearby and the day after her disappearance Christian B changed the registration of one of his vehicles.

He is also alleged to have confessed to a criminal associate, who was later arrested and told Scotland Yard about the confession.

Wolters has previously said the case is now a murder investigation and that he has discovered evidence that proves the three-year-old died in Portugal - however this has not been shared with Madeleine's parents Kate and Gerry.

Convicted paedophile Christian B is currently serving a seven-year sentence in a German jail for the rape of a woman in Portugal in 2005.

His lawyer Friedrich Fulscher said: "My client is innocent in the Madeleine case. The prosecutor keeps saying he is guilty but he hasn't interviewed him and hasn't shown us any of the evidence he says he has."