The prime suspect in the Madeleine McCann case has been ruled out of having any involvement in the rape and murder of another child.
Christian Brueckner was accused of being involved in the rape and murder of 11-year-old girl Claudia Ruf in his native home of Germany.
But DNA of the 43-year-old was no match for that found at the scene of Ruf's death.
It comes after police in Portugal failed to match the convicted paedophile to the rape of Irish tour guide Hazel Behan, 37.
A source told The Sun: "It is a setback, there's a sense of disappointment as this is the second time."
Portuguese police fear Brueckner will never be convicted for his suspected crimes against McCann.
Brueckner is currently in jail for drug offences and is appealing a seven-year sentence for raping a 73-year-old woman.
Sources told the Sun while police are working around the clock, leads have dried up.
"They know [he] will never talk. So it will be up to them to find the missing pieces of the jigsaw to lead them to finally find out what happened to Maddie."
Despite this, German officials say they have "concrete evidence" McCann is dead, and firmly believe Brueckner is behind her death.
But with leads drying up, Brueckner 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.
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."