Christian Brueckner, the prime suspect in the Madeleine McCann case, has boasted he's onto the police's strategies and won't fall their "dirty tricks" to get him to confess to having anything to do with the youngster's disappearance.
The 43-year-old paedophile and rapist is currently in jail for a range of drug offences, child abuse image charges and rape.
But Brueckner, who was in the vicinity when McCann disappeared from the resort while on holiday in Portugal in 2007, is reportedly raging over reports a fellow inmate may have been recruited by detectives to try and get him to confess.
The Sun reported that Portuguese Police are "concerned" at claims German authorities have resorted to "planting" spies inside the prison Brueckner is locked up in.
Brueckner is reportedly furious and says he's one step ahead of the police.
"Despite the silence of prosecutors, he is convinced that the police have been using all sorts of dirty tricks to try and nail him," a source told The Sun.
"He has been boasting there is no way he will fall for it. To him, the whole thing is a game of cat and mouse and he has remained silent throughout."
Portuguese Police claim German authorities are becoming desperate due to a lack of leads and evidence on Brueckner.
The source told The Sun the investigation has hit a brick wall and claims they are "resorting to sending people into prison to try and get him to confess".
Portuguese Police have said Brueckner isn't linked to McCann's disappearance, but the Germans remain convinced he is.
Two months ago Brueckner's lawyer Friedrich Fulscher hit out at officials, accusing them of creating a smokescreen.
He denied his client had "anything to hide" but says he will not co-operate with any investigation.
"Before our client starts to co-operate with the prosecutor's office, you could order holy water as a long drink in hell. That is not unusual. It is very normal not to talk to the police when you are suspected of committing a crime.
Brueckner could be freed from prison after serving his sentence for drug trafficking if the European Court of Justice believes an arrest warrant relating to Brueckner's rape of a 72-year-old woman in 2007 was legal.
The lawyer accused German prosecutors of staging the Hanover search as an attempt to swing opinion ahead of the decision by the European Court of Justice.
"I am very surprised they have started a search there now and not much earlier," Fulscher said.
"I was very surprised because the police had known for over two years that the garden was used by my client. I think the prosecutors are trying to influence the decision of the European Court by making bad media."