Fourteen of the 25 gang members who were convicted last Friday of kidnapping and murdering 23-year-old Ilan Halimi in 2006 are going to be retried, because their sentences were deemed too lenient.

The ringleader, Youssouf Fofana, was sentenced to life imprisonment and his sentence will stand. But other sentences were just six months long, and some were suspended.

The woman who seduced Mr Halimi, leading him to the gang, was sentenced to nine years in jail and could be freed in two.

Two gang members were acquitted altogether.

The sentences provoked an outcry by the victim’s family and members of the Jewish community, and Justice Minister Michele Alliot-Marie immediately asked the prosecution to appeal.

“The accomplices helped the killer massacre Ilan. They participated actively,” Mr Halimi’s mother Ruth said after the verdict. “What they did is terrible. They killed Ilan because he was Jewish. But the verdict is by no means exceptional.”

“The trial was a missed opportunity. It should have explored the facts, the construction of antisemitic stereotypes and the mechanism that led to the abduction, torture and killing of this young man,” Richard Prasquier, president of the Jewish umbrella group CRIF, said. “I was shocked by some of the sentences because they were not strong enough, not compared to what happened.

“The trial shouldn’t just be Fofana’s trial. His accomplices were part of it all. Any one of them could have put an end to this ordeal at any moment.”

Defence lawyers responded that the accused “were judged for their deeds and not to set an example”.

Throughout the trial, the defence lawyers were at pains to play down the antisemitic aspects of the crime.

Ilan Halimi was kidnapped three years ago by the “Gang of Barbarians”. They were hoping for a ransom, and targeted a Jew because he thought “they were rich”.

Mr Halimi was imprisoned in a basement while Fofana tried to negotiate with his parents. But the Halimis followed police orders and refused to pay.

After three weeks of physical torture, the gang stripped Mr Halimi, stabbed him and torched him, then abandoned him in a street. He died on the way to hospital.

The court decided that only two of the accused had antisemitic motives, Fofana and a guard who burned Ilan’s forehead with a cigarette.

And as the ruling came in on Friday night, friends and family of the defendants cheered at the short sentences. Fofana applauded the ruling.