When Emma Humphreys was acquitted of murder by the court of appeal in July 1995, it marked a change in the law in cases of abused women who kill violent men. Emma had stabbed Trevor Armitage, her violent boyfriend/pimp after he threatened her with a “gang bang”, and this vulnerable 16-year-old woman could take no more. In her short life she had already been witness to domestic violence, raped countless times, and prostituted while running away from a violent stepfather. At her appeal, following a three-year campaign by Justice for Women, lawyers argued that the provocation that led Humphreys to kill Armitage had built up over the years, and that all of the previous violence from men she had experienced should be taken into account.

But that change in the law did not benefit another vulnerable and abused young woman, Stacey Hyde, who was acquitted of murder yesterday, following a retrial. Hyde’s case begs the question: what are we doing to support young women who suffer male violence?

Vincent Francis, the deceased, had a history of violence towards women. The court at both trials accepted that there had been 27 previous acts of domestic violence towards his girlfriend, Holly Banwell, prior to the incident on the night he died, and that he had also attacked a former partner. At the retrial, Hyde’s lawyer described how Francis would regularly pull clumps of Banwell’s hair out by the roots, and likened the experience to “torture”.

I was in court to hear this evidence, and saw some jury members wince while being invited to imagine what this felt like. I also heard the 999 call made by Banwell on the night Francis was killed.

Stacey Hyde and Holly Banwell were friends, and they had been out drinking earlier that evening in September 2009, before returning to Banwell’s flat. In the early hours, Hyde woke up to hear Banwell screaming for help.

There is already clear evidence that women and girls are disbelieved when they report abuse

Francis had begun fighting with his girlfriend; Hyde apparently tried to intervene to help her friend, and during the 999 call Hyde is heard screaming in absolute terror as Francis attacks her. Watching from the press bench I could see Hyde cover her ears and lower her head each time the 999 call was played, and when the details of the violent attack on her were recalled. In the frightening events that followed this attack, which Hyde does not clearly remember, Hyde stabbed and killed Francis.

When the police arrived Hyde was very distressed, sobbing and saying, “He tried to kill me … I had to help Holly … he was going to kill her … I thought he would kill me …” Hyde was found to have injuries, some of which were consistent with previous self-harm, and some of which were consistent with a forceful struggle with Francis.

She was convicted of murder, but a new legal team obtained fresh evidence from adolescent psychiatrists that was presented to the court of appeal, and this conviction was quashed in November 2014. She had by then served five years of a life sentence with a nine-year tariff. The prosecution were not willing to accept a plea of manslaughter on the grounds of diminished responsibility and provocation, and insisted she should face a fresh trial for murder. Why was Hyde sent to retrial after the appeal court judges decided to overturn her conviction? Did the director of public prosecutions not wonder how a second trial, with all the associated stress and fear, might affect this extremely vulnerable young woman?

There is already clear evidence that women and girls are disbelieved when they report abuse – we saw this, for instance, in the Rochdale grooming cases. And there are also all sorts of signs that sexual and domestic violence is often regarded as a fuss about nothing (these include some judges’ comments in court, and the shockingly low conviction rates in such cases). To put Hyde, who suffered from a number of chronic mental health problems – including attention deficit hyperactivity disorder, borderline personality disorder, depression, and suicidal tendencies – through a second trial, when she had already served five years in prison, is nothing short of barbaric.

Her case is an example of how the failure to support young women who suffer mental health problems, sexual and domestic violence and childhood neglect can end in disaster.

Hyde had previously attempted suicide, self-harmed regularly, and been raped on more than one occasion. Her relationship with her mother was difficult, and the court at the retrial heard that Hyde was neglected and often verbally abused by her.

More often than not, young women with these problems harm themselves rather than others, but whatever the consequences of such failures, we need to be asking why we are letting women like Hyde down. The Crown Prosecution Service could have examined the evidence, decided that this was not a case of cold-blooded murder, and viewed it rather as one in which a terrified young woman protected herself and her best friend from a raging, violent man. They could have dropped the murder charges at the first, or indeed the second pre-trial hearing, and perhaps recommended that Hyde get help for her problems on the outside – not fight tooth and nail to secure a conviction and send her into the prison system.

To force Hyde to endure a second trial, with the prospect of her being reconvicted, was cruel and unnecessary. To vigorously oppose two bail applications after Hyde’s conviction had been quashed by the court of appeal, when there was evidence of suicidal tendencies, was plain wrong. The refusal of the DPP, and of the prosecutor in this case, to recognise that Hyde was a victim, not a murderer, shows that we have a long way to go before Emma Humphreys’ legacy is fully secure.