Investigators suspect Christian Brueckner, 48, played a part in young Madeleine vanishing from her family's holiday apartment in Praia da Luz, Portugal, in May 2007.
The woman, who has not been named, claims to have been a member of the German equivalent of the FBI who was at one stage wire-tapping the jail cell of convicted rapist Christian Brueckner.
Christian Brueckner, 48, who is currently serving a seven-year prison sentence in Germany for the 2005 rape of an American woman, is set to be released on September 17.
Madeleine McCann suspect Christian Brueckner has disturbingly taunted police in a new sickening letter about the toddler's disappearance as his prison release date looms closer.
This week masked police officers armed with pickaxes, shovels and even a mechanical digger could be glimpsed working their way through a neglected patch of Portuguese scrubland.
The ex-detective accused his own former police force of 'connivance' with 'shoddy' German cops in a foul-mouthed blast 24 hours after the start of a fresh operation to find Maddie's body
Convicted paedophile Christian Brueckner , 48, is the man German investigators believe abducted Madeleine from her family's rented holiday apartment in Portugal in 2007.
Christian Brueckner is currently in German jail for raping a woman in 2005 in the part of Portugal's Algarve region where three-year-old Madeleine McCann went missing in 2007.