Fabrice Burgaud, 34, was questioned about his investigation into the so-called Outreau paedophile affair by a cross-party committee of 30 deputies looking into ways of reforming the French justice system, so that a similar miscarriage of justice does not occur.
The affair began in 2001 with the arrest of a couple accused of sexually abusing their son in the northern town of Outreau.
Against a backdrop of the notorious Marc Dutroux scandal in neighbouring Belgium, neighbours and acquaintances were accused of taking part in an elaborate sex ring.
Of the 18 who went to trial, four were found guilty. Seven were acquitted at the July 2004 trial and six in an appeal hearing in December 2005, after which President Jacques Chirac publicly apologised for what he described as an "unprecedented judicial disaster".
Several of the victims of the scandal, who have accused Magistrate Burgaud of being naively fixated on establishing guilt and failing to listen to arguments in their defence, were present for the hearing.
Looking tired and drawn, the magistrate told the panel he was acutely aware of the victims' suffering -- but insisted he had done his job dutifully and said that other magistrates had rubber-stamped his decisions.
"I know this has shocked people ... but I repeat that I believe I did my job honestly without taking sides in any way," Magistrate Burgaud said.
However, the young judge admitted in an opening statement to the panel that he had "perhaps" made "errors of appreciation".
"I don't wish to avoid my responsibilities. I feel fully responsible for the investigation," he added.
The committee's work has sparked intense media interest in France, with millions tuning in last month to watch the nine men and four women describe their torment after the accusations were levelled against them.
Several spent long periods in jail before coming to trial.
Marriages were broken, jobs lost and children taken into custody. A 14th person committed suicide.
Deeper problems
But many politicians and jurists have said that Burgaud, who was 30 when he took charge of the case, should not be made a scapegoat for deeper problems in the French judicial process.
Among the issues under examination by the parliamentary committee:
- The reliability of evidence from alleged child victims in sex-abuse cases.
- The role of social workers and psychiatrists.
- The use of so-called "confrontations" in which accusers and accused are brought face-to-face before the investigating judge.
Under the French system, which also prevails in most European countries, an examining magistrate directs the police investigation, weighs up the arguments and then recommends whether or not to prosecute.
Some senior jurists have said the Outreau scandal proves the need to replace examining magistrates with a British-style system in which defence and prosecution argue it out in court.
"The examining magistrate must be abolished, because he wears two hats. He is both investigator and judge, and therefore caught in an intellectual contradiction. On one side he has to develop his investigation, and on the other he has to draw its conclusions," said top judge Renaud Van Ruymbeke.