Thousands of mourners have turned out for a silent march for a 11-year-old schoolgirl whose murder prompted widespread outrage when it emerged police had failed to question the suspected killer about previous child sexual abuse allegations.

The parents of the girl, who has been named only as Lyhanna, led the cortege on Sunday in the south-western village of Fleurance behind a banner reading “Never again”. Most of those who marched, including children, wore white shirts or T-shirts, many bearing a smiling portrait of the young victim.

Grief has been met with profound shock and anger. The killing has sparked a heated national debate over the delays and failings of France’s justice system after it emerged that the man being held in connection with Lyhanna’s disappearance and murder had been on the police’s radar since 2017.

The French president, Emmanuel Macron, acknowledged there had been an “unacceptable” failure in the legal system.

“We cannot ignore the fact that flaws have been exposed,” he said during a visit to Montenegro last week. “It is not a question of resources but responsibilities that will need to be determined through an official investigation.”

Lyhanna was last spotted getting into a grey car, identified as belonging to Jérôme Barella, a father of two and school cleaner, in Fleurance in the Gers département on 29 May. Her body was found seven days later in a disused grain silo 15km from where she went missing. Barella has denied killing her, telling police he had dropped her off at the local swimming pool.

After his arrest, it was discovered that, last August, the mother of a 10-year-old girl had gone to the police to allege that he had raped her daughter on several occasions. The preliminary investigation, containing interviews with the victim, psychological and medical reports confirming the child had injuries consistent with sexual abuse, and details of previous accusations against Barella, was sent by police in nearby Toulouse to the prosecutor’s office at Auch in January with an instruction to question him.

However, the prosecutor’s office reportedly failed to open the file for several weeks, then took a further six weeks to assign officers to the case. Barella had still not been contacted or summoned for questioning in the three months before Lyhanna was abducted and killed.

Other allegations have also emerged. In December 2017, a mother reported that her 17-year-old daughter had been in a relationship with Barella, but the case was dropped in 2018 after the girl said she had consented. In France a 17-year-old is considered able to consent.

In 2021, the suspect was fired from a cleaning job at another school for alleged inappropriate behaviour with a female student online.

In January 2022, he was accused of raping a seven-year-old child at his home in south-western France. The case was transferred to the local prosecutor but dismissed in 2024 owing to lack of evidence. The public prosecutor in the Gers town of Auch, Clémence Meyer, said inquiries, both medical and psychological, had not allowed police to verify the allegation.

A further accusation of rape was lodged last week but no details have been given.

France’s justice minister, Gérald Darmanin, said there was currently a backlog of 3m police complaints, of which 70,000 involve allegations of rape or sexual assault.

Darmanin, who instructed police last year to make sexual abuse cases a priority, said the breakdown in the legal system was “terrifying”.

“We failed to follow up on the complaints. I will take full responsibility for this. I am furious about this situation,” the minister told TF1.