Scotland Yard officers travelled to Malta to question Roderick MacDonald, 77, in his prison cell in a bid to uncover any vital clues on the Madeleine McCann disappearance, The Daily Record reports.
MacDonald was questions about his alleged connection to a child sex gang operating in Portugal, linked to her disappearance.
It is believed he was pressed on what he knew about a spate of burglaries which occurred in the Praia da Luz resort where Madeleine's family were staying when she went missing in 2007.
British detectives reckon the burglaries - believed to be carried out by a lone intruder between 2004 and 2010 - could be the key to finally solving what happened to her.
The latest development comes as it was confirmed 11 people - four of whom are thought to be British - due to be quizzed over Madeleine's disappearance next week will be asked to attend a police station as witnesses, not as suspects.
Scotland Yard said they would not give a "running commentary" on the investigation but their visit to MacDonald was confirmed by Maltese Government officials, the newspaper reports.
MacDonald was due to be extradited to the UK after he was remanded in custody in Malta.
But when detectives there searched his flat in the quiet village of Sannat they uncovered a stash of child pornography and sentenced him to 16 months in prison.
This forced Scotland Yard detectives to jet out to Malta in order to question him at the Corradino Correctional Facility outside the capital Valletta.
A close friend of MacDonald's, who had no idea about his sordid past, said: "He was always talking about how he was in the Algarve when Madeleine went missing.
"He would brag about how he sailed a yacht into Praia da Luz but we never thought anything of it.
"We had no idea how evil this man was before he was arrested. Now it seems completely sinister. No wonder the police were so keen to quiz him."
MacDonald, of Aldershot, Hants, was first arrested in the Algarve in 2010 and extradited to Australia where he was wanted for the 1998 rape of an eight-year-old.
He got six months' jail after accepting a plea deal for indecently assaulting the child then fled to Thailand after he was released.
After being deported to Britain by Thai authorities due to his history, MacDonald - previously known as Roderick William Robinson - settled in Brighton, East Sussex.
Despite being put on the sex offenders' register, he was convicted of molesting two girls, aged five and seven, on a boat at Sussex Yacht Club in 2012.
He fled abroad prior to his sentence and was handed a 12-month prison sentence suspended for two years in his absence.
When he was finally arrested in a dramatic swoop on his flat on the island of Gozo he is believed to have told detectives: "I should have spoken about all this years ago."