Marc Dutroux, who has been convicted of child murder, kidnap and rape, has a criminal record going back 25 years.
Dutroux was sentenced in 1989 to 13 years for abduction and rape
In 1979, the Belgian received the first of a series of convictions for theft, violent muggings, drug-dealing and trading in stolen cars.
Sexual crimes came later - in 1986, Mr Dutroux and his then-wife Michelle Martin were arrested for the abductions and rape of five girls, for which they were both imprisoned.
His own mother wrote to the prison director to warn about her son.
She complained that Mr Dutroux was using supervised visits to his grandmother's house to write up an inventory of the elderly woman's possessions, leaving her anxious and distressed.
"I have known for a long time and with good cause my eldest's temperament," she wrote.
"What I do not know, and what all the people who know him fear, it's what he has in mind for the future."
According to the French newspaper Liberation, the letters went unanswered.
Dutroux was born on 6 November 1956 in Brussels, the eldest
of five children.
His parents, Victor and Jeanine, were teachers who, he says, frequently beat
Certainly, his relationship with his parents was strained, and soon after they separated in 1971, he left home.
He became a drifter, and according to press reports, a homosexual prostitute.
By the time he was 20, Mr Dutroux was married to his first wife.
They had two sons, now in their early 20s, but she says he beat her and had affairs, and they separated in the early 1980s.
One of his mistresses was Ms Martin, who went on to become
his second wife and who is standing trial alongside Mr Dutroux
and two other alleged accomplices, on lesser charges.
The couple are now separated.
Crimes ranging from violent mugging to drug-dealing turned into a lucrative activity said to have helped him amass at least seven houses, according to the Associated Press.
He was sentenced to 13 years in 1989, but was released on parole after just three years in 1992, under a government scheme that was supposed to keep a close eye on sexual offenders in the community.
A panel of psychiatrists who analysed him after his arrest in 1996 found that Mr Dutroux did not fit the classic profile of a paedophile, according to the Associated Press.
"The age of the victims did not seem to arouse in him any given
effect or to play a particular role, beyond allowing him to kidnap
them, to manipulate them, to confine them," they said.
There were, however, warnings of his continued potentially dangerous behaviour.
It was some time soon after his release from prison that the former electrician, now receiving state benefits, started to build his basement "dungeon".
He went on to kidnap six girls between 1995 and 1996.
Only two of his victims, 12-year-old Sabine Dardenne and 14-year-old Laetitia Delhez, were found alive.