The adoptive parents of Christian Brückner were forced to send him to a home for troubled teenagers when they could no longer cope with his behaviour, neighbours have claimed.
Brigitte and Fritz Brückner are said to have brought him up “as one of their own” after he was abandoned as a young boy.
But they were unable to handle the disruptive behaviour of their adoptive son, who is now the key suspect in the disappearance of Madeleine McCann.
German prosecutors earlier this week announced that a 43-year-old man, named only as Christian B in German media, is being investigated on suspicion of murdering three-year-old Madeleine.
She vanished in 2007 while on holiday with her family in Praia de Luz, Portugal.
Brückner, who is currently serving a prison sentence for separate offences, has also been connected to a string of other missing children’s cases in Germany and Belgium.
Speaking from her home in Bergtheim, Bavaria, Mrs Brückner denied any knowledge of his lurid past.
“I don’t know anything about it, I don’t want to know anything about it,” she told MailOnline.
Neighbours in the family’s small village praised the couple, who they claimed were left little choice but to send Brückner away to a reform school because he was such a “handful”.
“The Brückners were a lovely couple, very kind, but what happened with their boy Christian is a catastrophe,” one neighbour said.
“They took him in as a baby and brought him up as one of their own. He was often in trouble and he got worse and worse as he grew up into a teenager.”
Mrs Brückner brought him up alone after her husband suffered life-changing injuries in a car accident.
“Brigitte did her best, but she could not cope with the boy and look after her husband,” the neighbour added.
“Christian had been in trouble and that is when he was sent to a reform school for delinquent teenagers in Würzburg.”
Another neighbour, a mother of three who knew Brückner growing up, said: “He was well known in our area for getting into trouble. Everyone knew that he was a handful and it was not easy for his parents.
“I was fully aware of the Madeleine McCann case. I was horrified when I heard that the suspect is from a family that lives over the road from me.”