Ten French men have been acquitted and four have received short sentences over the gang-rape of teenage girls in a trial described by one of the victims' lawyers as a "judicial shipwreck".

In a case that has shocked France and cast a light on a culture of youth sexual violence, two women now in their twenties said that as teenagers they had endured months of almost daily gang-rapes by scores of men in Fontenay-sous-Bois outside Paris. The case was seen as the tip of the iceberg of a wider problem of gang-rapes by youths on poor estates.

After a four-week trial, four of the accused were found guilty of taking part in gang-rapes but 10 were acquitted. Those found guilty were handed sentences that ranged from three years' suspended sentence to one year in prison. Because of time already served on remand, only one man was returned to prison after the verdict.

The sentences were far lighter than those recommended by the state prosecutor, who had called for prison sentences of five to seven years for eight of the men – which was already seen as slight. The court found one of the woman, identified as Nina, was raped, but did not uphold rape allegations against the second, identified as Stephanie.

Clothilde Lepetit, one of the women's lawyers, described the verdicts and sentencing as "a judicial shipwreck" for the women. She denounced what she called the extremely poor handling of the investigation and the judicial failings of the trial.

Another lawyer for the women, Laure Heinich, asked: "What sentence makes sense when one hears that gang-rapists are given a three years suspended sentence?"

The case, which has gripped the country, has highlighted the problems in historic rape investigations where material evidence is lacking and much rests on the women's word. Lawyers for the women said they felt the women's testimony had not been respected during the trial.

Amid surprise at the verdict in France, the justice minister, Christiane Taubira, said there could be grounds to appeal. "Personally, I'm shocked by gang-rapes, by every form of aggression against women and I think we have to create conditions so that the facts are established and those guilty can be effectively identified."

The women's minister, Najat Vallaud-Belkacem, said the case had shown that better education on sex and sexuality was needed in schools.

The alleged Fontenay-sous-Bois attacks took place between 1999 and 2001. One night returning from a cinema, aged 16, Nina, described as a tomboy who was good at school, said she was grabbed by a local group of youths, taken to basement cellars in the flats, raped and subjected to a series of brutal sex attacks by scores of local boys. The extremely violent, prolonged sex attacks by large groups of boys continued daily, in car-parks, stairwells, apartments, cellars and the empty playground of a local nursery school. She said there would be "at least 25" youths present during attacks in which she screamed, protested, cried and vomited. One witness described 50 boys "queuing" to attack her.

Threatened that her flat would be burned down if she spoke out, she was afraid to tell her mother, who noticed she was washing eight to 10 times a day.

The women kept quiet for years about the attacks until 2005, when Nina was left unconscious by one final brutal beating following years of abuse and finally told a female police officer. Psychiatric experts had agreed that both women were the victims of rape. Nina has put on 70kg (11 stone) since the attacks, describing the weight-gain as a "shell" behind which to hide. Stephanie attempted to kill herself a few days into the trial, which was held behind closed doors because the defendants were minors at the time of the rapes.

The women were hailed by their lawyers for their bravery in speaking out against a "culture of silence" surrounding sexual violence against girls on estates.

Some of the acquitted men spoke anonymously to French media to say they were relieved at the verdicts.