MADELEINE McCann suspect Christian B has made another early jail release bid claiming the case is based on an "unreliable" witness.
His lawyer said the main witness against his client is a criminal who swapped information for police favours.
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Friedrich Fulscher said the informant who claimed suspect Christian B confessed his guilt to him may have done so in order to get help.
The witness is thought to have told detectives that 43-year-old German drifter Christian B told him in a bar that he knew what had happened to Madeleine, who was three at the time she vanished from a Portuguese holiday apartment in 2007.
Mr Fulscher believes the informant may later, in return for telling cops this information, have got early release from a sentence he was serving in a foreign country.
Mr Fulscher told Sky News: "If this is the same person, I think it's the worst witness you can get.
"A human who has spent his whole life cheating people for his own benefit is never a reliable witness."
...I think it's the worst witness you can get. A human who has spent his whole life cheating people for his own benefit is never a reliable witness.Lawyer Friedrich Fulscher
Christian B, whose full name cannot be fully identified under German privacy law, is the target of German prosecutor Hans Christian Wolter.
Mr Wolter has publicly said he believes Christian abducted and killed Madeleine, but does have enough evidence to charge him.
This week he said was still looking for vital evidence against Christian B, but has not questioned his suspect.
Mr Fulscher said Christian B's reputation would now be forever tarnished as many people would always consider him responsible for Madeleine's disappearance.
He said: "If you pee in the same place long enough it will stink. And that's definitely what's happening in the Christian B case.
"He won't be able to lead a normal life at any point, without being recognised and facing hostility.
"A prosecutor who goes public (during an investigation) knows that. He can destroy a reputation and it was taken very lightly in this case."
He won't be able to lead a normal life at any point, without being recognised and facing hostility.Lawyer Friedrich Fulscher
Christian B has a list of previous convictions including rape, child sex offences, theft and dishonesty.
'NO INNOCENT LAMB'
Mr Fulscher said: "Of course, he is no 'innocent lamb', he has made many mistakes in his past which have been punished by the law - and that is completely right.
"It is a basic principle of our system that someone who has served his sentence can claim his right to be part of society again.
"I don't think he is someone who has done everything right in his life, but that doesn't mean that you can suddenly condemn him for things he hasn't done."
Christian B is in jail in Kiel, northern Germany, serving seperate sentences for rape and drug trafficking.
He is eligible for parole after serving 14 months of a 21 month sentence for drug trafficking and his lawyer has already filed a request with authorities demanding his release.
Mr Fulscher explained: "He is isolated 23 hours a day in a 7sqm cell. He is allowed out to exercise for one hour a day.
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"That is because a prisoner accused of these kind of crimes, and who is known in the jail, is in danger of being attacked by other inmates.
Mr Fulscher added that since acting as his lawyer he has noticed his client has been "getting slimmer" due to his lack of movement.