Madeleine McCann suspect Christian Brueckner once reportedly told a former friend he had "accidentally killed" his ex-girlfriend.
The man, called Aberle, said Christian Brueckner, 44, admitted he had killed the woman when he was drunk, the Sun reports.
Aberle is understood to have told cops in 2010, at about the same time prostitute Monika Pawlak, 24, was mutilated and stuffed in two bin bags.
Brueckner was investigated over the death of Pawlak, who worked in a kitchen and occasionally as a prostitute, in Hanover in 2010, but he was never charged.
The latest detail reportedly emerged during a meeting between German and Portuguese officers reviewing the case of Madeleine's tragic disappearance back in 2007.
He was ordered to give a DNA sample during a mass DNA test.
Brueckner is currently serving a seven-year prison sentence for raping a 72-year-old American woman in Praia da Luz in 2005, about 18 months before Madeleine went missing.
The Mirror last month reported how investigators are "100% sure" sex offender Christian Brueckner murdered Madeleine McCann.
They have the evidence to charge him and hope the probe will conclude next year.
Speaking exclusively to the Mirror, German prosecutor Hans Christian Wolters said: “We’re confident we have the man who took and killed her.”
Madeleine was only three when she disappeared while on a family holiday in Praia da Luz, Portugal in 2007.
