An inmate may have been recruited by German prosecutors to get Christian Brueckner to confess he was behind Madeleine McCann’s disappearance.
German legal sources say an “informer” could have been employed as investigators tried to get evidence to charge Brueckner.
Asked about the claim tonight, the public prosecutor’s office would not deny it, simply saying: “No comment.”
Sources said the inmate was recruited when Brueckner was in Wolfenbuettel jail before being transferred to Kiel, where he is now in solitary confinement.
It happened before Brueckner, 43, was named as the prime suspect after phone records placed him in Praia da Luz in Portugal on the night Madeleine, three, vanished in 2007.
Alexander Stevens, an expert on German criminal law, said investigators’ chances of finding any new evidence was now low.
He said: “The only remaining possibility to convict Christian B. would be to obtain information about fellow prisoners.
“The prosecutor had apparently wanted to get the accused to confess.”
If the claims, which were made in a respected German newspaper, are true, it could cause problems for the public prosecution office in Braunschweig.
This is because according to paragraph 136a of the German Code of Criminal Procedure, a statement must not be obtained by the investigating authorities by any type of deception.
It has also emerged that British police have been given more cash for the investigation into Madeleine’s disappearance, taking the total to in excess of £12million.
The latest Home Office grant to the Met’s Operation Grange is believed to be around £350,000 and will cover the inquiry until March 2021.
Brueckner was named in June as the prime suspect in Madeleine’s abduction.
He is in jail for drug offences and has been convicted of child pornography offences and rape.