Carine and Gino Russo, whose eight-year-old daughter Melissa died of starvation in the basement of Dutroux's home nearly six years ago, were the first to withdraw their representation in the prosecution.
"There are just too many things which have been done badly or not at all, or done the wrong way round," said the couple's lawyer Victor Hissel.
According to the daily La Libre Belgique, the parents of Julie Lejeune, who was found buried with Melissa in Dutroux's backyard in August 1996, have also now decided to withdraw.
Correspondents say the decision of the parents to renounce their representation in the prosecution is a great embarrassment for the authorities.
It is likely to fuel existing suspicions that officials seriously bungled the investigation and sought to cover up any potential connections with establishment figures.
The case is due to go to court next year.
Humiliation
After Dutroux was arrested and charged with the kidnap and murder of four young girls in 1996, police and officials were accused of gross incompetence for not picking him up in the first place.
He had been released on parole after an earlier conviction for raping five girls, and despite a string of tip-offs, police failed to make the connection between him and the abductions.
Their greatest failure came when officers searched his home, but failed to find Melissa and Julie.
The pair starved to death after Dutroux was arrested on a completely separate issue.
Officials have also been accused of mistreating the parents of the victims, and of failing to pass vital information between prosecutors and police.
The police faced further humiliation in 1998 when Dutroux succeeded in escaping for three hours after overpowering an officer who was guarding him.
Left leads
While in custody, Dutroux admitted being involved in the four abductions - and in kidnapping two other girls who were found alive.
But he has insisted he had had nothing to do with murdering Melissa and Julie, or two other girls, 17-year-old An Marchal and 19-year-old Eefje Lambreks, who were found in the house of one of his alleged accomplices, Bernard Weinstein.
Earlier this year, he accused the Belgian police and justice system of refusing to investigate leads he provided them with, and claimed he was only one part of a larger paedophile network.
This allegation was largely backed by parents of the victims, but dismissed by the authorities.
The refusal of officials to investigate Dutroux's allegations became a source of serious contention between the two sides.