The French Justice Minister apologised yesterday for bizarre and disturbing events at a child sex trial in northern France that have led to widespread condemnation of the country's methods of investigating and judging complex crimes.

The French Justice Minister apologised yesterday for bizarre and disturbing events at a child sex trial in northern France that have led to widespread condemnation of the country's methods of investigating and judging complex crimes.

Seven defendants, who had spent up to three years in jail awaiting trial, were yesterday cleared of all wrong-doing by a jury at Saint-Omer, near Boulogne. Six other defendants, including a priest, were convicted of sexual assaults on children, despite the apparent collapse of all credible evidence against them.

Two couples who admitted abusing their own, and each other's children in adjoining flats in a council estate at Outreau, near Boulogne, were given lengthy jail sentences. Lurid accusations made by one of the four, Myriam Delay, led investigators to believe the couples were part of an international, child-sex ring, with tentacles across the nearby Belgian border.

Mme Delay withdrew these allegations in the middle of the trial, then withdrew her withdrawal, before admitting a second time that she had concocted her testimony against neighbours and acquaintances to spread the guilt for her own crimes. Other evidence against the majority of the defendants, given by the child victims and several child psychology experts, also appeared to be discredited under cross-examination.

Defence lawyers, families of the accused and the French press expressed stupefaction yesterday when the jury, after 17 hours of deliberations, acquitted seven of the 13 defendants incriminated, then cleared, by Mme Delay but convicted the six others.

One lawyer, Eric Dupond-Moretti, whose client was acquitted, said the verdict was illogical and incomprehensible. "There was the same absence of evidence, the same staggering vacuity at the centre of the accusations against all these defendants," he said. Blandine Lejeune, lawyer for the 67-year-old priest, Father Dominique Wiel, who was jailed for seven years, longer than the prosecution had requested, said her client had been "contaminated by calumny" in the minds of the jury. All lawyers for the other convicted defendants said they would appeal, except the counsels for the couples who admitted child abuse.

At a press conference in Paris yesterday, the Justice Minister, Dominique Perben, apologised to the seven defendants who were cleared, two of whom had spent almost three years in jail awaiting trial. "This must not happen again," M. Perben said, without specifically addressing the case of the six defendants who were convicted on slight or non-existent evidence.

M. Perben said he was setting up a working group to examine changes to the justice system, including a new right of appeal for anyone held for more than six months without trial.

French press commentators and leading jurists have pointed to the Outreau trial as a clear condemnation of weaknesses in the justice system: the habit of placing suspects in jail to try to extract confessions and the reliance on juges d'instruction or "investigating magistrates" to examine both sides of a case.

In the Outreau investigation, the critics said, a young and inexperienced investigating judge, influenced by the Dutroux child-sex and murder scandal in Belgium, set out to prove, on slight evidence, that there was a paedophile network in northern France.

The judicial system has also come under fire, even in conservative newspapers, including Le Figaro, for closing ranks and failing to confront its apparent mistakes.

When the public prosecutor decided to ask for convictions and jail sentences against some of the defendants incriminated by Mme Delay, there was a chorus of disbelief in the French press. Most people assumed the jury would acquit everyone but the two couples at the centre of the affair. But a confused and divided jury appears to have obeyed the prosecutor.